PIN Photodiode | It’s working Principle, Construction, VI Characteristics.

pin photodiode

What Is PIN Diode?

A PIN photodiode is a specialized semiconductor device that converts light energy into an electrical current.

It is widely used in various applications, ranging from optical communications and sensing to medical imaging and scientific research.

The unique structure and operating principle of a PIN photodiode make it a versatile and efficient light detector.

Read more about Photo Diode click here

Characteristics Of PIN Photodiode

  1. Reverse Bias Operation:
  • PIN photodiodes are typically operated under reverse bias voltage, meaning the P-side is connected to the positive terminal and the N-side to the negative terminal.
  • The reverse bias voltage increases the width of the depletion region, enhancing the light absorption capability of the photodiode.
  • 2. Fast Response Time:
  • PIN photodiodes have a fast response time, allowing them to detect and respond to light signals quickly.
  • The fast response time is crucial for applications that require the detection or modulation of high-frequency light signals.
  • High Sensitivity:
  • PIN photodiodes are highly sensitive to light, enabling them to detect even low-level light signals or weak light intensities.
  • This high sensitivity makes them suitable for applications that require accurate detection in low-light conditions or demanding environments.
  • Low Noise:
  • PIN photodiodes exhibit low noise characteristics, minimizing the interference or distortion of weak light signals during detection.
  • low noise performance is essential for applications that require high signal-to-noise ratios and precise measurements.
  • Wide Spectral Response:
  • PIN photodiodes exhibit a broad spectral response range, making them capable of detecting light across a wide range of wavelengths.
  • The specific spectral response range depends on the material used in the photodiode.
  • Different semiconductor materials can be chosen to optimize the photodiode’s response for specific wavelength ranges.

Construction Detail of a PIN Photodiode:

A PIN photodiode is constructed using three distinct layers of semiconductor material: the P-type layer, the Intrinsic layer, and the N-type layer. Each layer contributes to the photodiode’s unique functionality. Here is a detailed description of the construction of a PIN photodiode:

  1. P-type Layer:
  • The P-type layer serves as the outermost layer of the photodiode structure.
  • It is typically doped with trivalent impurities, such as boron (B), which creates an excess of holes (positive charge carriers) in the material.
  • The P-type layer provides the positive terminal connection for the photodiode.

2. Intrinsic Layer:

  • The Intrinsic layer is sandwiched between the P-type and N-type layers and is the central layer of the photodiode.
  • It is usually made of undoped or lightly doped semiconductor material, such as silicon (Si) or germanium (Ge).
  • The Intrinsic layer is responsible for the light absorption process and the generation of electron-hole pairs when illuminated by photons.
  • It has a wider depletion region compared to other layers, enabling efficient charge separation.

3. N-type Layer:

  • The N-type layer is located adjacent to the Intrinsic layer and forms the opposite side of the photodiode structure from the P-type layer.
  • It is doped with pentavalent impurities, such as phosphorus (P), which introduces an excess of electrons (negative charge carriers) into the material.
  • The N-type layer provides the negative terminal connection for the photodiode.

4. Depletion Region:

  • The Intrinsic layer, which is lightly doped, creates a depletion region between the P-type and N-type layers.
  • The depletion region is a region depleted of majority charge carriers (holes and electrons) due to the diffusion and electric field effects.
  • The width of the depletion region is determined by the applied reverse bias voltage across the photodiode.
  • The depletion region plays a critical role in the separation of electron-hole pairs generated by incident photons.

The construction of a PIN photodiode allows for efficient light absorption and charge separation. Incident photons that penetrate the depletion region of the Intrinsic layer create electron-hole pairs, and the electric field across the depletion region causes them to move in opposite directions, generating a photocurrent.

Working Principle of PIN photo diode

The working principle of a PIN photodiode is based on the generation and separation of electron-hole pairs in a semiconductor material when exposed to light. Here is a detailed explanation of the working principle of a PIN photodiode:

  1. Incident Light:
    • When light photons with sufficient energy strike the Intrinsic layer of the PIN photodiode, they are absorbed by the semiconductor material.
    • The absorption of photons transfers their energy to the electrons in the valence band, promoting them to the conduction band, creating electron-hole pairs.
  2. Electron-Hole Pair Generation:
    • The absorbed photons in the Intrinsic layer generate electron-hole pairs through the process of optical absorption.
    • The electrons are excited from the valence band to the conduction band, leaving behind holes in the valence band.
  3. Depletion Region:
    • The PIN photodiode’s structure includes a depletion region, which is the region between the P-type and N-type layers.
    • The depletion region is a region depleted of majority charge carriers (holes in the P-type and electrons in the N-type regions) due to the combined effects of diffusion and electric field.
  4. Electric Field:
    • When a reverse bias voltage is applied to the PIN photodiode, the electric field is established across the depletion region.
    • The electric field drives the electrons towards the N-side and the holes towards the P-side of the photodiode.
  5. Charge Separation:
    • The generated electron-hole pairs in the Intrinsic layer experience the electric field across the depletion region.
    • The electric field causes the electrons to drift towards the N-side and the holes to drift towards the P-side, facilitating charge separation.
  6. Photocurrent Generation:
    • The separated electrons and holes contribute to the flow of current in the external circuit connected to the PIN photodiode, resulting in a photocurrent.
    • The photocurrent is proportional to the incident light intensity and the efficiency of the absorption and charge separation processes.
  7. Output Signal:
    • The generated photocurrent can be measured and processed to obtain information about the incident light, such as intensity or modulation.

VI characteristics of PIN photo diode

The VI characteristics of a PIN photodiode describe the relationship between the voltage applied across the photodiode and the resulting current flowing through it. The VI characteristics provide important information about the photodiode’s behavior and performance. Here is an explanation of the VI characteristics of a PIN photodiode:

  1. Dark Current:
    • When no light is incident on the photodiode, a small current called the dark current flows through it.
    • The dark current is primarily caused by thermal generation of electron-hole pairs within the semiconductor material.
    • It is typically very low in PIN photodiodes but increases with temperature.
  1. Reverse Bias Region:
    • In the reverse bias region, a reverse voltage is applied across the PIN photodiode.
    • The reverse bias voltage extends the depletion region, enhancing the photodiode’s light absorption capability.
    • As the reverse bias voltage increases, the depletion region widens, allowing for more efficient collection of photo-generated charge carriers.
    • In this region, the photodiode acts as a current source, and the resulting current is the photocurrent generated by the incident light.
    • The photocurrent is directly proportional to the intensity of the incident light.
  2. Photocurrent Saturation:
    • In the reverse bias region, the photocurrent initially increases with increasing reverse bias voltage.
    • However, there is a saturation point beyond which further increases in reverse bias voltage do not significantly affect the photocurrent.
    • The saturation occurs when the depletion region encompasses the entire Intrinsic layer, and additional voltage does not contribute to further widening of the depletion region.
  3. Breakdown Region:
    • If the reverse bias voltage continues to increase beyond the saturation point, the PIN photodiode may enter the breakdown region.
    • In the breakdown region, the photodiode experiences a sharp increase in current, known as the breakdown current.
    • This is an undesirable operating region for a photodiode as it can cause permanent damage and degrade the device’s performance.

Application of PIN photo diode

  1. Optical Communications:
    • PIN photodiodes are widely used in optical communication systems, including fiber-optic communication networks.
    • They serve as light detectors, converting optical signals into electrical signals for data transmission and reception.
    • PIN photodiodes offer high responsivity, fast response times, and low noise characteristics, making them ideal for high-speed communication applications.
  2. Photovoltaic Power Generation:
    • PIN photodiodes can be used as photovoltaic devices to convert light energy directly into electrical energy.
    • They are utilized in solar cells and photovoltaic modules to generate electricity from sunlight.
    • PIN photodiodes with high sensitivity to specific wavelengths can be tailored for efficient energy conversion in various solar cell designs.
  3. Environmental Sensing:
    • PIN photodiodes are employed in environmental sensing applications, such as light level detection, ambient light sensing, and light intensity monitoring.
    • They can be used in automatic brightness control (ABC) circuits for displays, ambient light sensors in smartphones and tablets, and light sensors in smart home automation systems.
  4. Imaging and Scanning:
    • PIN photodiodes play a vital role in imaging applications, including digital cameras, surveillance systems, and medical imaging devices.
    • They convert light signals into electrical signals, allowing for the capture and processing of images.
    • PIN photodiode arrays are used for high-resolution imaging and scanning applications, such as barcode readers and document scanners.
  5. Scientific Research:
    • PIN photodiodes are utilized in scientific research for light detection and measurement in various experiments and instruments.
    • They can be employed in spectrometers, radiometers, and light meters for precise measurement of light intensity and spectral analysis.
  6. Industrial and Automotive Applications:
    • PIN photodiodes find use in industrial applications such as laser alignment, industrial inspection, and quality control systems.
    • They are also used in automotive applications, including optical sensors for proximity detection, rain sensing, and ambient light detection.

Advantages and disadvantages of pin photo diode

PIN photodiodes offer several advantages and disadvantages, which are important to consider when choosing them for a specific application. Here are the advantages and disadvantages of PIN photodiodes:

Advantages:

  1. High Sensitivity: PIN photodiodes have high sensitivity to light, allowing them to detect even low light levels accurately. They can capture weak optical signals effectively.
  2. Wide Spectral Response: PIN photodiodes have a wide spectral response range, enabling them to detect light across a broad range of wavelengths. This makes them suitable for applications that require detection of different wavelengths of light.
  3. Low Dark Current: PIN photodiodes typically have low dark current, which is the current flowing through the photodiode in the absence of light. Low dark current leads to higher signal-to-noise ratios and improved sensitivity.
  4. Fast Response Time: PIN photodiodes have fast response times, allowing them to quickly convert light signals into electrical signals. This makes them suitable for applications that require high-speed detection or modulation.
  5. Low Noise: PIN photodiodes exhibit low noise characteristics, leading to more accurate and reliable signal detection. Low noise allows for improved performance in applications where small signals need to be detected.
  6. High Quantum Efficiency: PIN photodiodes have high quantum efficiency, meaning they can efficiently convert incident photons into electrical current. This makes them suitable for applications where high sensitivity and efficient light conversion are critical.

Disadvantages:

  1. Large Size: PIN photodiodes tend to be larger in size compared to other photodetector types. This can limit their use in applications that require compact or miniaturized designs.
  2. Capacitance Effects: PIN photodiodes have inherent capacitance, which can cause a decrease in response time and limit their use in high-frequency applications.
  3. Temperature Dependence: The performance of PIN photodiodes can be influenced by temperature variations. Changes in temperature can affect the dark current and quantum efficiency of the photodiode.
  4. Power Consumption: PIN photodiodes require a reverse bias voltage to operate, which can consume power. This power consumption needs to be considered in low-power or battery-operated applications.
  5. Breakdown Voltage: PIN photodiodes have a maximum reverse bias voltage, beyond which they can enter the breakdown region and become damaged. Care should be taken to avoid exceeding the breakdown voltage during operation.

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What is a PIN photodiode?

A PIN photodiode is a type of photodetector that consists of three layers: P-type, Intrinsic (I) layer, and N-type. The Intrinsic layer is lightly doped, allowing it to have a larger depletion region for efficient light absorption.

How does a PIN photodiode work?

When photons (light) enter the depletion region of a reverse-biased PIN photodiode, they generate electron-hole pairs. These charge carriers are swept across the depletion region, resulting in a photocurrent. The magnitude of the photocurrent is proportional to the intensity of the incident light.

What are the advantages of using a PIN photodiode?

Some advantages of PIN photodiodes include high sensitivity to light, wide spectral response, low dark current, fast response times, low noise characteristics, and high quantum efficiency.

What are the applications of PIN photodiodes?

PIN photodiodes find applications in optical communications, photovoltaic power generation, environmental sensing, imaging and scanning devices, scientific research, industrial and automotive applications, and more.

Are PIN photodiodes temperature-sensitive?

Yes, PIN photodiodes can exhibit changes in their electrical characteristics with temperature variations. This can include shifts in dark current, responsivity, and quantum efficiency.

Can PIN photodiodes operate at high frequencies?

PIN photodiodes may have limitations in terms of their response time at high frequencies. The device’s capacitance and transit time of carriers can cause slower response to rapidly changing optical signals.

What is Photodiode? Its operations and applications

What Is Photodiode?

A photodiode is a p-n junction semiconductor diode that is always operated in reverse-biased conditions. It is a special type of diode called a light detector or photodetector. It is used to convert light signals into electrical signals.

Photo diode

Symbol of Photodiode

The photodiode symbol is very similar to the normal p-n junction diode except that it contains arrows striking the diode. The arrows striking the diode represent light or photons. It has two terminals Anode and Cathode.

Characteristics of Photodiode

  1. Photodiode should be always operated in reverse bias condition.
  2. Applied reverse bias voltage should be low.
  3. It generates low noise
  4. High gain
  5. High response speed
  6. High sensitivity to light
  7. Low sensitivity to temperature
  8. Low cost
  9. Small size
  10. Long lifetime

Types of Photodiode

There are various types of photodiodes available in the market. The working of different types of photodiodes works in a slightly different way, but the basic operation of these diodes remains the same. The types of photodiodes can be classified based on their construction and functions as follows.

  • PN junction Photodiode
  • Schottky Photo Diode
  • PIN Photodiode
  • Avalanche Photodiode

Operating principle of Photodiode

When a P-N junction diode is reverse-biased, a reverse saturation current flows due to the thermally generated hole and electron being swept across the junction as the majority carriers. With the increase in temperature of the junction, more and more holes and electron pair are generated and so the Reverse Saturation Current Io increases. The same effect was had by illuminating the junction. When photon (light energy) bombards a p-n junction, it dislodged (knocks) valance electrons. The more photon (light) striking the junction the large the reverse current in a diode. It is due to the generation of more and more charge carriers with the increase in the level of illumination.

V-I Characteristics of Photodiode

The VI characteristic curve of a photodiode represents the relationship between the voltage (V) across the photodiode and the current (I) flowing through it.

Here’s a general description of the behavior of a photodiode’s VI characteristic curve:

  1. Dark Current Region: When no light is incident on the photodiode, it typically exhibits a small leakage current known as the dark current. In this region, the current is relatively low, and the voltage may be close to zero or have a slight reverse bias.
  2. Photocurrent Region: When light falls on the photodiode, it generates electron-hole pairs, leading to an increase in the current flow. As the incident light intensity increases, the current through the photodiode also increases, resulting in a positive slope in the VI characteristic curve.
  3. Saturation Region: At higher light intensities, the current reaches a saturation point where further increases in light intensity do not significantly affect the current. The VI characteristic curve levels off in this region, indicating that the photodiode has reached its maximum response.

It’s important to note that the specific shape of the VI characteristic curve can vary depending on the characteristics of the photodiode, such as its material, size, and operating conditions. Additionally, different types of photodiodes, such as PIN photodiodes or avalanche photodiodes, may exhibit slightly different behaviors in their characteristic curves.

Photodiode Operation Modes

The photodiode can be operated in one of the two modes, namely Photovoltaic mode, Photoconductive mode.

Selection of operation mode of photodiode is depends upon the speed requirements of the application and the amount of dark current that is tolerable.

Photovoltaic Mode: 

This mode is also known as zero-bias or unbiased mode, In this mode no external voltage is applied to the photodiode. Dark current is very low in photovoltaic mode. In photovoltaic mode the speed of operation of photodiode is very low .

The photodiodes operated in photovoltaic mode are generally used for low speed applications or for detecting low light levels.

Photoconductive Mode:

 In photoconductive mode photodiode usually operated in reverse biased. The reverse voltage application will increase the depletion layer’s width, which in turn decreases the response time & the junction capacitance. This mode is too fast and displays electronic noise.

Why photodiode operated in reverse biased condition?

In reverse biased condition the only current flowing through the diode in the absence of light the reverse saturation current which is very small in magnitude. Hence the change in diode current due to the light incident on it is significant (photocurrent is in microampere). If diode is forward biased then the forward current in the absence of light would be in mA and change in the forward current due to light will not be even noticeable. Hence the photodiode operated in reverse biased condition.

Advantages of Photodiode

  1. High sensitivity – This mean, a large change in the photocurrent for a small change in light intensity.
  2. High speed of operation as compared to LDR (Light Dependent Resistor).
  3. High gain

Disadvantages of Photodiode

1.Dark current increases with temperature.

2. Poor temperature stability.

3. External bias voltage is essential for operation.

4. Amplification is required, as the output current is small magnitude.

Applications of Photodiode

  1. In cameras for sensing the light intensity.
  2. In the fiber optical receiver.
  3. In light intensity meters.

Types of diodes read here

Q1: What is a photodiode?

A photodiode is a semiconductor device that converts light energy into electrical current. It operates in reverse bias, and when light falls on the diode, electron-hole pairs are generated, resulting in a current flow.

Q2: How does a photodiode work?

Photodiodes work based on the principle of the photovoltaic effect. When photons of sufficient energy strike the semiconductor material of the diode, they create electron-hole pairs. The electric field established by the reverse bias voltage causes the electrons to move towards the anode, generating a photocurrent.

Q3: What are the important characteristics of a photodiode?

Key characteristics of photodiodes include responsivity (sensitivity to light), quantum efficiency (ratio of generated charge carriers to incident photons), dark current (current in the absence of light), reverse bias voltage, response time, spectral response, and noise characteristics.

Q4: What are the different types of photodiodes?

There are various types of photodiodes available, including PN photodiodes, PIN photodiodes, avalanche photodiodes (APDs), and Schottky photodiodes. Each type has different performance characteristics and is suitable for specific applications.

Q5: Can photodiodes be used in reverse bias mode?

Yes, photodiodes are typically operated in reverse bias mode to improve their performance. Reverse biasing increases the depletion region, enhances the response time, reduces capacitance, and improves linearity and sensitivity.

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Advantages and disadvantages of Zener diode shunt voltage regulator

Zener Diode Shunt Voltage Regulator Circuit

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Zener Diode and Its working, Characteristics and Applications.

How Zener diode work as a voltage regulator.

Advantages of Zener diode shunt regulator are given below:

  • For wider range of load currents and input voltages the Zener diode shunt regulator provide a better regulation.
  • It gives higher current capability.
  • The Zener voltage regulator is very economic.
  • It requires only two or three components.
  • It has a very simple circuit.

Disadvantages of Zener diode shunt regulator are given below:

  • Internal impedance of the Zener shunt voltage regulator circuit is high.
  • The voltage regulation is poor.
  • The output voltage in Zener shunt voltage regulator is not adjustable because the output power of Zener shunt regulator is depending on Zener voltage. It means VO ­= VZ.
  • The Zener shunt voltage regulator cannot be used for large load current.
  • Zener shunt voltage regulator has poor efficiency for heavy loads because a large amount of power is wasted in Zener diode resistance (R2) and series resistor (RS) in comparison with load power.
  • The output voltage of Zener regulator slightly changes due to Zener resistance
  • In Zener shut regulator changes in load current produce changes in Zener current. As a result, the output voltage also changes.

Light Emitting Diode (LED): It’s Construction, Working and Application

LED is a heavily doped p-n junction diode which converts electrical energy into light energy. The diode can emits light under forward bias condition. The process of emitting light in response to the strong electric field or flow of electric current is called Electroluminescence. The LED’s are made up of a special type of semiconductor materials such as Gallium Arsenide (Ga As), Gallium Arsenide Phosphide  (Ga As P), Gallium phosphide (Ga P).

Light Emitting Diode

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Symbol Of LED

The light emitting diode is a specially doped  p-n junction diode which emits light when electric current passes through it in forward direction. In the LED, the recombination of charge carrier takes place. The electron from the N-side and the hole from the P-side are combined and gives the energy in the form of heat and light.

The LED’s are made up of a special type of semiconductor materials such as Gallium Arsenide (Ga As), Gallium Arsenide Phosphide  (Ga As P), Gallium phosphide (Ga P).

Silicon and Germanium are not used for LED’s because they are heat producing materials and are very poor in producing light.

The forward voltage ratings of LEDs is from 1V to 3 V and forward current ratings is from 10 to 80 mA. The switching speed of LED is very high 1ns.

Symbol Of LED

The circuit symbol of LED is shown in figure given below. LED symbol is very similar to a normal p-n junction diode symbol with two small arrows that indicate the emission of light, thus it is called light-emitting diode (LED). The LED having two terminals namely anode (+) and cathode (-). 

Symbol of LED

Basics Structure Of LED

The Structure of a LED is very different from that of a normal P-N junction diode. The PN junction semiconductor chip ( LED chip ) of an LED is surrounded by a transparent, hard plastic epoxy resin hemispherical shaped shell . Which protects the PN junction of an LED from vibration and shock.

Structure of LED

The outer cover of LED is constructed in such a way that the light emitted by the junction are reflected away from the surrounding substrate base to which the diode is attached and are focused upwards through the domed top of the LED, which itself acts like a lens concentrating the amount of light. Because of this emitted light appears to be brightest at the top of the LED.

There are five major structure of LED (Light emitting diode) these are-

  1. Dome LED
  2. Planer LED
  3. Surface Emitter LED
  4. Edge Emitter LED
  5. Supper luminescent LED

Out of these five structures of LED, first two structures (dome LED and Planer LED structure) are type of homojunction LED’s. That produce invisible light which is mostly used in T.V remote control and industrial counting. And last three structures ( Surface Emitter LED, Edge Emitter LED, Supper luminescent LED ) are heterojunction LED used as a light source in Optical Fiber Communication System.

The main part of LED is a LED chip. LED chip is nothing but a p-n junction semiconductor chip. It consist of a p-type semiconductor and a n-type semiconductor. When p-n type semiconductor is join a junction is form called p-n junction and a depletion region is form near the junction due to concentration gradient of electron and hole in p-n type semiconductor. And a potential barrier is develop across the junction. This potential barrier opposes the flow of electrons from n-type semiconductor and flow of holes from p-type semiconductor.

LED Chip

To overcome the potential barrier, a external voltage is apply which is greater than the potential barrier of depletion layer. If the applied voltage is greater than the potential barrier of the depletion layer, the electric current starts flowing.

Working principle of LED (Light Emitting Diode)

The working of Light Emitting Diode (LED) is very similar to normal p-n junction diode. When LED is forward bias, the majority carrier electron of the n- type and the majority carrier hole of the p-type move across the junction. As a result, electron-hole recombination take place. Due to this recombination energy release in the form of light. This recombination of electron and hole takes place in depletion region as well as in p-type and n-type semiconductor.

Light Emitting Diode (LED)

The LED’s are made up of a special type of semiconductor materials such as Gallium Arsenide (Ga As), Gallium Arsenide Phosphide  (Ga As P), Gallium phosphide (Ga P) they are light producing materials. Where as normal p-n junction diode is made up of silicon and germanium they are heat producing materials and are very poor in producing light.

Principle of Electroluminescence

LED ( light emitting diode ) work on the principle of electroluminescence. Electroluminescence is a process of converting electrical energy into (nonthermal) light.

When the LED is forward biased, the electrons in the n-region will cross the junction and recombine with the hole in the p-type material.

These free electrons reside in the conduction band and hence at a higher energy level than the holes in the valance band. The electrons in the higher energy level (conduction band) will not stay for long time. So, after a short time period, these electron return back to the lower energy level (valance band) and while ,returning back to the valance band energy releases in the form of a light or photon. This process is called electroluminescence. In this way LED emits light.

The semiconductor material with large forbidden energy gap emits high intensity light whereas the semiconductor material with small forbidden energy gap emits low intensity light. So we can say that, the intensity of the emitted light is depends on the material used for constructing LED and forward current flow through the LED.

Operating Principle of LED

LED biasing

The Voltage drop across a conducting LED is the range of 1 V to 3 V, depending on the material used. This voltage is much higher then that of conventional diode. The current rating of the LED is 10 to 80 mA.

When we applied forward voltage across LED in between 1 V to 3 V, LED start conduct and emitted light.  However, if the applied forward voltage across LED is increased greater than 3 volts. The depletion region in the LED breaks down and suddenly large electric current flow through the device. This sudden large current may destroy the device.

LED is forward bias

To protect the LED from damage a resistance Rs is connected in series with LED, this resistance is called current limiting resistance. This resistor restricts the flow of extra current through the LED which may destroy the LED.

Output characteristics of LED

The output characteristics curve of LED is linear. It means the amount of emitted by the LED is directly proportional to the applied forward current across the LED. More the applied forward current , the greater is the emitted output light. 

Output characteristics curve of LED

Colour of the emitted light

The colour of the emitted light is decided by the material use to construct an LED. We know that, every colour having different wavelength. The wavelength of light or colour depends on the value of forbidden gap (Eg). Forbidden gap (Eg) value is depend on the type of material used in LED.

  • Gallium Arsenide (GaAs) – infra-red
  • Gallium Arsenide Phosphide (GaAsP) – red to infra-red, orange
  • Aluminium Gallium Arsenide Phosphide (AlGaAsP) – high-brightness red, orange-red, orange, and yellow
  • Gallium Phosphide (GaP) – red, yellow and green
  • Aluminium Gallium Phosphide (AlGaP) – green
  • Gallium Nitride (GaN) – green, emerald green
  • Gallium Indium Nitride (GaInN) – near ultraviolet, bluish-green and blue
  • Silicon Carbide (SiC) – blue as a substrate
  • Zinc Selenide (ZnSe) – blue
  • Aluminium Gallium Nitride (AlGaN) – ultraviolet

Silicon and Germanium are not used for LEDs because their forbidden gap do not allow the light emission in visible spectrum.

The most common available LEDs emit green, red, yellow, orange and blue colour.

Some LEDs are capable of emitting infrared light which is not visible to human eyes.

Advantages Of LED

  • LED are small in size and light weight. Therefore it is possible to pack large number of LED in a small space while manufacturing a display.
  • They are available in different spectral colours.
  • They have longer life as compared to the lamp.
  • The light emitted by an LED is proportional to the amount of current flowing through it. Hence we can control the current flowing through LED to vary their brightness as per the requirement of the application.
  • The switching speed of LED is high less than 1ns. So it is suitable at high operating speed applications.
  • LEDs are very economical and easily available.
  • The quantum efficiency of LED is high.
  • It has better linearity. The input output characteristics curve of LED is linear.
  • LED is less temperature dependent.

Disadvantages of LED

  • Output power is affected by changes in temperature.
  • LED need large power for their operation as compare to normal p-n junction diode .
  • Luminous efficiency of LED is low.
  • Overcurrent can damage LED easily.

Application Of LED

  • LED work as a indicators in various electronic circuits.
  • LED used in infrared remote control.
  • LED used in traffic signal.
  • LED used in digital watches.
  • LED used in automotive heat lamps
  • LED used in Camera flashes.
  • LED used in seven segment and alphanumeric displays.

Difference between a normal Diode and a LED

Normal Diode LED
1. The semiconductor device like a diode conducts simply in one direction.The LED is one type of diode, used to generate light.
2. The designing of the diode can be done with a semiconductor material & the flow of electrons in this material can give their energy the heat form.The LED is designed with the gallium phosphide & gallium arsenide whose electrons can generate light while transmitting the energy.  
3. The diode changes the AC into the DCThe LED changes the voltage into light
4. It has a high reverse breakdown voltageIt has a low-reverse breakdown voltage.
5. The on-state voltage of the diode is 0.7v for silicon whereas, for germanium, it is 0.3vThe on-state voltage of LED approximately ranges from 1.2 to 2.0 V.
6. The diode is used in voltage rectifiers, clipping & clamping circuits, voltage multipliers.    The applications of LED are traffic signals, automotive headlamps, in medical devices, camera flashes, etc.

Zener Diode as a voltage regulator

Zener Diode Shunt Voltage Regulator circuit

A Zener diode is a special purpose p-n junction diode that is designed to operate in the reverse direction. They are heavily doped p-n junction diode. Hence, it has very thin depletion region near the junction. When reverse voltage applied across the Zener diode a small reverse current flow through the device called reverse leakage current.

As the reverse voltage is increase continuously, at a certain value of reverse voltage, the junction will be breakdown and drastically a large reverse current flow through the device. This breakdown is called Zener breakdown. The voltage at which this breakdown occurs is called Zener voltage ( Vz ). To protect the diode from this large reverse bias current a resistor (Rs) is connected in series with diode. This resistor is called current limiting resistor . This reverse bias property of Zener diode is used in voltage regulation.

Symbol of Zener Diode
V-I Characteristic of Zener Diode

Read more: Zener Diode

What is a voltage regulator?

Voltage regulator is a circuit that has an ability to maintain constant output voltage across load either input voltage is varying or load current is varying. 

Consider the following circuit of simple shunt Zener regulator.

Shunt Voltage Regulator Circuit

To understand the working more effectively some important points must be remembered-

  1. To get effective voltage regulation, the input voltage Vi must be greater than the Zener voltage Vz.
  2. The value of series resistor or current limiting resister Rs must be such that in no-load condition, it must protect the Zener diode from over current, as in this condition, I=Iz since IL=0.
Reverse Bias characteristic of Zener Diode

Check out Hindi video on how Zener diode work as Voltage Regulator?

Mathematical

There are 3 currents in the circuit, these are I, Iz and IL.

I=Iz+IL… using Kirchhoff’s Current Law

Iz =(Vi−Vz)/R… using Ohm’s law

IL=Vo/RL=Vz/RL…

because, Vz= Vo as Zener diode is connected in parallel with the load resistor RL

Working of Zener voltage regulator circuit

Find three possible conditions for the given circuit

  1. When input voltage Vi and load resistance RL both are constant.
  2. When input voltage Vi is constant but load resistance RL is varying.
  3. When input voltage Vi is varying but load resistance RL is constant.

All three cases are explained as follows:

Cases #1: Let us assume that Vi and RL are constant:

We know that,

                        I = Iz + IL… using Kirchhoff’s Current Law

In this condition, I and IL are both are constant, so Iz is also constant. So, the circuit remains in steady state condition. However, this condition is considered only for understanding the working. But practically, this condition may not exist in regulator circuit.

Case #2: Now assume that Vi is constant, but RL is varying:

We know that,

                        I = Iz + IL… using Kirchhoff’s Current Law

In this condition, input current I is constant, but IL is varying, since RL is also varying. So, there are two possible conditions here.

  1. Let us assume  RL increases. Then IL decreases. But input current I is constant, because we have assumed that Vi is constant. And as I=Iz+IL. So Iz increases proportionally to adjust this condition.
  2. Let us assume RL decreases. Then IL is increases. But input current I is constant as Vi is constant. And as I=Iz+IL so Iz decreases proportionally to adjust this condition again.

Important Point:  Here RL=0 condition is not assumed, because if RL=0, then IL=∞ so Iz=0 and then the regulation process will collapse.

Case #3: Assume that Vi is Varying, but RL is constant: 

We know that,

                        I = Iz + IL… using Kirchhoff’s Current Law

In this condition, input current I is varying, but IL remains constant, since RL is constant. So, there are two possible conditions here.

  1. Let us assume Vi increases. Then I increase. But load current IL remains constant, because we have assumed that RL is constant. And as I=Iz+IL so Iz increases proportionally to adjust this situation.
  2. Let us assume  Vi decreases. Then I decrease. But load current IL remains constant, as RL is constant. And as I=Iz+IL so Iz decreases proportionally to adjust this situation, again.

Important Point: Here if RL=∞ i.e., load is removed from the circuit, then IL=0 so Iz=I. Hence at the starting I have already told, that the value of series resistor R must be properly selected.

In this way, in any possible conditions of the circuit, i.e. when input voltage and load resistance both are changing, the above conditions will work effectively. Thus in all cases, the zener diode maintains constant output voltage across the load RL.

Important Note: All the given conditions are applicable only when Vi >> Vz.

Frequently Ask Questions FAQ’s –

What is voltage regulator?

Voltage regulator is a circuit that has an ability to maintain constant output voltage across load either input voltage is varying or load current is varying. 

What is Zener Diode?

A Zener diode is a heavily doped PN junction diode that is designed to operate in the reverse direction.

What is Zener Breakdown?

The Zener breakdown mainly occurs because of a high electric field. When the high electric-field is applied across the PN junction diode, then the electrons start flowing across the PN-junction. Consequently, expands the little current in the reverse bias.

What is difference between Zener Diode and normal P-N junction diode?

The main difference between a normal P-N junction diode and Zener diode is normal P-N Junction allows current to flow only in one direction while Zener diode allows current to flow in both directions.

Applications of Zener Diode

Zener diodes are used for voltage regulation, as reference elements, surge suppressors, and in switching applications and clipper circuits.

Zener diode

Definition

A Zener diode is a heavily doped PN junction diode that is designed to operate in the reverse breakdown region

A Zener diode is a special purpose p-n junction diode that is designed to operate in the reverse direction. When reverse voltage applied across the Zener diode (anode terminal is negative w.r.t cathode terminal) and the potential reaches the Zener Voltage (knee voltage), the junction breaks down and the current flows in the reverse direction. This effect is known as the Zener Effect.

The breakdown voltage of a Zener diode is carefully set by controlling the doping level during manufacture.

The name Zener diode was named after the American physicist Clarence Melvin Zener who discovered the Zener effect.

Read More What is Diode and its Working?

Read More V-I characteristics of p-n junction diode.


Symbol of Zener diode

Symbol of Zener diode

Circuit Diagram or layer structure of Zener Diode

Zener diode is always connected in reverse direction because it is specifically designed to work in reverse direction. The reverse biasing means the anode of the diode is connected to the positive terminal of the supply and the cathode is connected to the negative terminal of the supply. The depletion region of the diode is very thin because it is made of the heavily doped p and n type semiconductor material.

Circuit diagram or layer structure of Zener diode

Zener diode video explained in Hindi.


Working of Zener Diode

Zener diode is heavily doped than the normal p-n junction diode. Hence, it has very thin depletion region.

When Zener diodes work in forward biased condition it work like a normal p-n junction diode. However, In reverse biased condition a small leakage current flows through the diode. This current is called reverse leakage current or also called reverse saturation current.

If this reverse biased voltage across the diode is increased continually, high electric field develop across the junction. This strong electric field break all the covalent near the junction and the junction breakdown and a large reverse current starts flowing through the diode. This large reverse current may damage the diode. To protect the diode from damage a resistance is connected in series with Zener diode that resistance is called current limiting resistance (Rs). This breakdown is called Zener breakdown. The voltage at which this breakdown occurs is called Zener voltage (Vz). If the applied reverse voltage across the diode is more than Zener voltage, the diode provides a conductive path to the current through it. Hence there is no chance of further avalanche breakdown in it.


V-I characteristics of Zener diode

The VI characteristic of the Zener diode is shown in the figure below. When the diode is connected in forward bias, this diode work like a normal diode. But When a reverse voltage is applied across the diode. initially a small reverse saturation current Io flows across the diode. As the reverse voltage is increased, at a certain value of reverse voltage, the junction will be breakdown and drastically a large reverse current flow through the device. This breakdown is called Zener breakdown. The voltage at which this breakdown occurs is called Zener voltage.

VI characteristics of Zener Diode

Application of Zener Diode

The Zener diode is mostly used as a voltage regulator or voltage stabilizers, voltage reference, clipping circuits, overvoltage protection etc.

  • Zener diode is used as a voltage regulator or voltage stabilizers: The Zener diode is used for regulating the output voltage. It provides the constant output voltage from the fluctuating input voltage. The Zener diode is connected in parallel across the load and maintain the constant voltage VZ and hence stabilizes the voltage.

Read More: Zener Diode as a Voltage Regulator

  • Zener diodes are used in clipping circuits: Zener diodes are used to modify or shape AC waveform clipping circuits. The clipping circuit limits or clips off parts of one or both of the half cycles of an AC waveform to shape the waveform or provide protection.
  • Zener diode in overvoltage protection: If the input voltage increases to a value higher than the Zener breakdown voltage, current flows through the diode and create a voltage drop across the resistor; this triggers the SCR and creates a short circuit to the ground. The short circuit opens up the fuse and disconnects the load from the supply.

English video on what is Zener Diode?


Frequently Ask Questions FAQ’s –

What is Zener Diode?

A Zener diode is a heavily doped PN junction diode that is designed to operate in the reverse direction.

What is Zener Breakdown?

The Zener breakdown mainly occurs because of a high electric field. When the high electric-field is applied across the PN junction diode, then the electrons start flowing across the PN-junction. Consequently, expands the little current in the reverse bias.

What is differenece between Zener Diode and normal P-N junction diode?

The main difference between a normal P-N junction diode and Zener diode is normal P-N Junction allows current to flow only in one direction while Zener diode allows current to flow in both directions.

Applications of Zener Diode

Zener diodes are used for voltage regulation, as reference elements, surge suppressors, and in switching applications and clipper circuits.

Advantages of Zener Diode

Power dissipation capacity is very high
• High accuracy
• Small size
• Low cost

What is current limiting resistance?

To protect the diode from damage a resistance is connected in series with Zener diode that resistance is called current limiting resistance (Rs).

What is Zener Voltage?

The breakdown voltage in the Zener diode when connected in the reverse biased is called Zener voltage.
The Zener diode holds its Zener voltage so steady and constant, it has huge application in circuits, most importantly, voltage regulation.

Schottky Diode (Hot Carrier Diode)


Definition

“A Schottky Diode is a metal-semiconductor diode with a low forward voltage drop and a very fast switching speed”

What Is Schottky Diode ?

The Schottky Diode is another type of semiconductor diode but have the advantage that their forward voltage drop is less (0.15 to 0.3V) than that of the conventional silicon pn-junction diode (0.6 to 0.7V). Schottky diode is also known as Schottky barrier diode, surface barrier diode, majority carrier device, hot-electron diode, or hot carrier diode.

In a conventional P-N junction diode, a P-type semiconductor and an N-type semiconductor are used to form the P-N junction. When a P-type semiconductor is joined with an N-type semiconductor, a junction is formed known as P-N junction.

Where as Schottky diode is a metal-semiconductor diode. When a metals (such as aluminum, platinum, gold, tungsten) and N-type semiconductor is joined, a junction is formed between metal and N-type semiconductor. This junction is known as a M-S junction or metal-semiconductor junction. A metal-semiconductor junction formed creates a barrier or depletion layer known as a Schottky barrier.

Schottky diode is a unipolar device because in Schottky diode both the metal and n-type semiconductor have electrons as their majority carriers, as almost negligible holes are present in a metal. i.e., electrons are responsible for conduction. Hence it is a unipolar device.

Where as normal p-n junction diode is a bipolar device because in normal p-n junction diode p-type semiconductor have majority carrier holes and n-type semiconductor have majority carrier electrons. So here both electrons and holes are responsible for conduction. Hence it is called bipolar device.

P-N Junction Diode

Schottky Diode

The Schottky diode is named after German physicist Walter H. Schottky.

Schottky diode can switch on and off much faster than the normal p-n junction diode. Also, the Schottky diode produces less unwanted noise than normal p-n junction diode. These two characteristics of the Schottky diode make it very useful in high-speed switching applications.

Just like a conventional P-N junction diode, a Schottky diode will conduct a current in the forward direction when sufficient forward voltage is applied. But a silicon PN junction diode has a typical forward voltage of 0.6–0.7 Volts, while Schottky’s forward voltage is 0.2–0.3 Volts.

Symbol of Schottky Diode

The symbol of the Schottky diode is shown in the figure below.

Here, the anode is the metal side and the cathode is the semiconductor side.

Symbol Of Schottky Diode

Construction Of Schottky Diode 

Schottky Diode are formed by joining n-type semiconductor substrate and a metal. This metal and semiconductor junction is called M-S Junction. The metal used for fabrication of Schottky diode can be gold, tungsten, platinum silver etc . This M-S junction creates a barrier or depletion layer known as a Schottky barrier.

Two types of Schottky barriers are formed near the junctions these are Rectifying and Non-rectifying type. When a metal is joined with lightly doped n-type semiconductor this is called non-ohmic contact. In non-ohmic contact a large depletion region is formed near the junction this will create large Schottky barrier  across the junction and this Schottky barrier is called rectifying Schottky barrier. Sequentially When a metal is joined with heavily doped n-type semiconductor this is called ohmic contact. In ohmic contact a thin or negligible depletion region is formed near the junction this will create small Schottky barrier  across the junction and this Schottky barrier is called non-rectifying Schottky barrier.  

So we can say that, the non-rectifying metal-semiconductor junction or ohmic contact offers very low resistance to the electric current whereas the rectifying metal-semiconductor junction or non-ohmic contact offers high resistance to the electric current as compared to the ohmic contact.

Working of Schottky Diode

Unbiased Schottky diode

When the metal is combined with the n-type semiconductor , the free electrons in the n-type semiconductor will move from n-type semiconductor to metal. Device will reached to its equilibrium state. When free electrons moves across the junction, it provides an extra electron to the atoms present in the metal. Due to this, atoms present in the metal junction receive an extra electron and become negative ions. 

The atoms at n-side junction lose electrons and become positive ions. Thus, positive ions collected near the n-side junction and negative ions collected near the metal junction. These positive and negative ions create a depletion region near the junction. The width of the depletion region is is negligibly thin in metal as compare to n-type semiconductor. This depletion region will create a potential barrier near the junction, and this potential barrier is called Schottky barrier. This barrier stopped the movement of electron across the junction.

To overcome this barrier, the free electrons need energy greater than the built-in-potential across the junction.

Forward biased Schottky diode

In forward biased metal is connected with positive terminal of battery and n-type is connected with negative terminal of battery. When forward bias voltage is applied, a large number of free electrons are generated in the metal and n-type semiconductor. If the applied forward biased voltage is less than the built-in-potential (i.e. 0.2 volts ) across the junction, no free electrons in n-type semiconductor and metal move cross the junction. 

If the applied voltage is greater than built-in-potential (i.e. 0.2 volts ) , the free electrons gain enough energy and overcomes the built-in-potential of the depletion region. Due to this , electric current starts flowing through the Schottky diode.

So Schottky diode have low forward turn on voltage (0.2 to 0.3 Volts) as compare to normal p-n junction diode forward turn on voltage (0.3 to 0.7 volts).

This lower forward voltage requirement enables Schottky diodes to have higher switching speeds and increased efficiency.

Reverse biased Schottky diode

In Reverse biased metal is connected with negative terminal of battery and n-type is connected with positive terminal of battery.

When reverse bias voltage is applied, a large depletion region grow across the junction. Due to this, large potential barrier developed across the junction.  As a result, the electric current stops flowing the device. However, a small reverse leakage current flows through the device due to the thermally excited electrons in the metal.

When further in increased in reverse bias voltage, the depletion region become weaker and current start increasing gradually. If high reverse bias voltage is applied the junction will be breakdown and suddenly large revers current flow across the device. Which may permanently damage the device.

V-I Characteristics of Schottky diode

The V-I characteristics of Schottky diode is shown figure below. The V-I characteristics of Schottky diode is almost similar to the P-N junction diode. The forward voltage drop of Schottky diode is very low (0.2 to 0.3 volts) as compared to the normal P-N junction diode (0.6 to 0.7 volts).

The turn-on voltage for a Schottky diode is very low as compared to the p-n junction diode. If the forward bias voltage is higher than 0.2 or 0.3 volts, electric current starts flowing through the Schottky diode.

In Schottky diode, the reverse saturation current occurs at a very low reverse bias voltage as compared to the silicon p-n junction diode.

Features Of Schottky Diode:

  • Higher efficiency
  • Low forward voltage drop
  • Low capacitance
  • Low profile surface-mount package, ultra-small
  • Integrated guard ring for stress protection

Difference between Schottky diode and normal p-n junction diode

  • Schottky diode is a unipolar device because in Schottky diode both the metal and n-type semiconductor have majority carriers electrons. Here, electrons are responsible for conduction. Where as normal p-n junction diode is a bipolar device because in normal p-n junction diode p-type semiconductor have majority carrier holes and n-type semiconductor have majority carrier electrons. So here both electrons and holes are responsible for conduction.
  • The depletion region is negligible or absent in case of Schottky diode, whereas in p-n junction diode the depletion region is present.
  • Schottky diode reverse breakdown voltage is very small as compared to the normal p-n junction diode.
  • The forward voltage drop of Schottky diode is very less as compared to normal p-n junction diode.
  • The switching Speed of Schottky diode is higher than normal p-n junction diode. Because the forward on state voltage drop of Schottky diode is low as compare to normal p-n junction diode.

Applications of Schottky diodes

  • Schottky diode Used in radio frequency (RF) applications.
  • Schottky diode Used in Switched-mode power supplies (SMPS).
  • Schottky diode Used in various protection circuits.
  • Schottky diode Used in voltage clamping application.
  • Schottky diode Used in RF mixer and Detector diode.
  • Schottky diode Used in solar cell application.
  • Schottky diode used in logic circuits (like TTL and CMOS logic circuits).

Frequently Asked Questions

What is Schottky diode?

A Schottky Diode is a metal-semiconductor diode with a low forward voltage drop than the P-N junction diode  and a very fast switching speed.

What is the difference between schottky diode and normal pn junction diode

Why is the Schottky diode called a hot-carrier diode?

when electrons are energized then jumped over a metal which is has high energy state. Due to this high energy metal involvement it is called hot carrier diode.

Why the p-n diode is called minority carrier device and Schottky diode is called majority carrier device?

According to definition, device using both majority and minority charge carriers are called minority carrier device. For example, PN diode uses both holes and electrons as charge carrier.
Device using only one type of charge carriers is called Majority Carrier Device. Fire example, Schottky diode which uses only electrons as charge Carrier.

Applications of Schottky diodes

Schottky diode Used in radio frequency (RF) applications.
Schottky diode Used in Switched-mode power supplies (SMPS).
Schottky diode Used in various protection circuits.
Schottky diode Used in voltage clamping application.
Schottky diode Used in RF mixer and Detector diode.
Schottky diode Used in solar cell application.
Schottky diode used in logic circuits (like TTL and CMOS logic circuits).

Diode: SYMBOL, TYPES, WORKING, Characteristics & Applications

Please check video lecture on what is Diode, symbol, working and Its applications

What is Diode ?

Diode is a two electrode or two terminal electronics device, that conducts current only in one direction. So we can say that diode is a unidirectional device which allows the flow of current in only one direction while blocks the flow of current in opposite or reverse direction. It is work like a switch.

An ideal diode act as a perfect conductor with zero resistance in forward direction and act as a perfect insulator with infinite resistance in reverse direction. But Practically no diodes can be act as a ideal diode, always they offer a low resistance in forward direction and very high resistance in the reverse direction.

The most common type of diode is P-n Junction semiconductor diode. The diode is made either of the two semiconductor materials, silicon or germanium. For designing the diodes, silicon is more preferred over germanium because silicon semiconductors diode works at higher temperature compared with germanium diode.

Diode having two terminal anode and cathode. Diode is said to be “forward biased” when anode is positive w.r.t. cathode, So current flow in forward direction. So we can say that diode is in conducting state (offer low resistance forward direction). Diode is said to be “Reverse biased” when cathode is positive w.r.t. anode, So no current flow in reverse direction. So we can say that diode is in non-conducting state (offer high resistance reverse direction).

Symbol Of Diode

The symbol of diode is given below, a triangle adjoining the line. The arrowhead in the symbol points the direction of electric current flow through the device . Diode having two terminal anode and cathode. The anode terminal is connected to the p side and the cathode terminal is connected to the n side.  

Formation of Diode

To create a simple p-n junction diode we take a n-type semiconductor and a p-type semiconductor material. In n-type semiconductors, free electrons are the majority charge carriers where as in p-type semiconductors, holes are the majority charge carriers. When the n-type semiconductor is joined with the p-type semiconductor, a p-n junction is formed. And a depletion layer is formed near the junction. The width of depletion layer is depend on the doping level of semiconductor material. Depletion layer is thick in lightly doped semiconductor material and thin in heavy doped semiconductor material. The terminal connected to the p-type is the anode. The terminal connected to the n-type side is the cathode.

Formation of p-n junction

Biasing of Diode

To make the current to flow through the diode, It is necessary to “bias” the diode. “The process of applying the external DC voltage to a p-n junction semiconductor diode is called biasing”.

  • Zero Biased Diode
  • Forward Biased Diode
  • Reverse Biased Diode

Zero Biased Diode (Unbiased Diode)

Zero biased p-n junction diode means when no external DC voltage applied to the terminals.

Now let as see what happen when no external DC voltage applied to the terminals. To create a simple p-n junction diode we take a n-type semiconductor and a p-type semiconductor material. In n-type semiconductors, free electrons are the majority charge carriers where as in p-type semiconductors, holes are the majority charge carriers.

When the n-type semiconductor is joined with the p-type semiconductor, a p-n junction is formed. And a depletion layer is formed near the junction due to concentration gradient. Now due to concentration differences, majority carriers diffuse from one side to another.

As the concentration of holes is high in the p-type region and it is low in the n-type region, the holes start diffusing from the p-type region to the n-type region. In the Same way, as the concentration of electrons is high in the n-type region and it is low in the p-type region, the electron start diffusing from the n-type region to the p-type region and recombine with holes available there. Each electron diffusing into the “p” side will leave behind a positive immobile ion on the n-side.

When an electron combine with a hole on the “p” side, an atom which accepts this electron, loses its electrically neutral status and becomes a negative immobile ion. Due to tis recombination process, large number of positive immobile ion accumulate near the junction on the n-side and large number of negative immobile ion accumulate near the junction on the p-side.

The negative charged ion on the p-side will start repelling the electrons which attempt to diffuse into p-side and after some time diffusion will be stop completely . At this point junction is said to be in equilibrium state.

zero biased p-n junction diode

Forward Biased Diode

In forward biased p-n junction diode p-region (anode) connected to positive terminal of the external DC source and n-region (cathode) connected to negative terminal of the external DC source the the biasing is said to be forward biasing .

Forward Biased Diode

Due to the negative terminal of external source connected to the n- region, free electrons from n- side are pushed towards the p- side. Similarly the positive end of the supply will push holes from p- side toward the n- side.

With increasing in the external supply V , large number of holes (p-side) and electrons (n-side) start travelling towards the junction. As the result of this, the width of depletion region will reduce. Due to reduction in the depletion region barrier potential also reduce. And a particular value of supply voltage depletion region will collapse. Hence large number of majority carrier (electrons and holes) can cross the junction and large current will flow that current is called forward current from anode to cathode.

Reverse Biased Diode

In reverse biased p-n junction diode p-region (anode) connected to negative terminal of the external DC source and n-region (cathode) connected to positive terminal of the external DC source the the biasing is said to be reverse biasing .

Reverse Biased Diode

Due to the reverse biased, holes in the p-region are attracted toward negative terminal of supply and move away from the junction. Similarly electron in the n -region are attracted toward positive terminal of supply and move away from the junction.

Due to this moment of electron and hole away from the junction the width of the depletion region increases and barrier potential will also increased resulting no current flow through the device. But a small current flow through the diode called reverse saturation current due to the moment of minority carrier. If this reverse applied voltage continuously increases after a certain reverse applied voltage a large revers current flow through the device & the depletion layer will be destroyed. The external voltage at which the the depletion layer will be completely destroyed that voltage is called Revers Breakdown Voltage. When junction breakdown take place large reverse current flow across the device. If this revers current not limited by a external resistance it will destroyed the diode. 

Applications of Diode

The various applications of diodes are :-

  • Diode is work like a switch : A p-n junction diode is used as electronic switch in digital logic circuits.
  • Diode also work as a Rectifier : A p-n junction diode can be used to convert the alternating current (AC) to the direct current (DC).
  • Diodes in Logic Gates: Diode also use in many digital logic gates to perform logic operations.
  • Diodes in Clamping Circuits: A clamper circuit is used to shift or alter either positive or negative peak of an input signal to a desired level. This circuit is also called as level shifter or DC restorer. These clamping circuits can be positive or negative depends on the diode configuration.
  • Diodes in Clipping Circuits: The clipper circuit is used to put off the voltage beyond the preset value without disturbing the remaining part of the input waveform. Based on the diode configuration in the circuit, these clippers are divided into two types; series and shunt clipper.

Types Of Diode

  1. Light Emitting Diode (LED)
  2. P-N junction diode
  3. Zener diode
  4. Schottky diode
  5. Avalanche diode
  6. Photodiode
  7. Laser diode
  8. PIN diode
  9. Varactor diode
  10. Tunnel diode