The basic building blocks of electronic components are semiconductor materials, multiple types of semiconductor devices are available for different circuit applications. In this article, we discuss a special semiconductor device called PIN DIODE.
A Pin diode is almost like our general-purpose p-n junction diode, but a pin diode had a great difference in technical and physical specifications compare to other semiconductor devices.
In this post, we include different information’s about pin diodes such as its internal structure, construction details, working, symbol, and applications of pin diodes.
symbol of pin diode
The symbolic representation of the pin diode is the same as the p-n junction diode, the positive side represents with anode and the negative side represents the cathode.
Pin photodiode symbol
When we represent the pin photodiode with a symbol, it’s the same as a p-n junction semiconductor with an anode and cathode indication. An incoming light arrow is symbolized with a pin diode symbol.
A pin diode is just like a p-n junction diode, a p-type and n-type materials are separated with an intrinsic semiconductor is the internal specification of Pin diode.
The name pin diode represents much important information’s about the device, which is ‘P’ represents p-type semiconductor, ‘I’ represent intrinsic semiconductor and ‘P’ represents p-type semiconductor.
When we consider each of the layers individually, at p-type semiconductor layer holes is the majority carriers that means the p-type layer is heavily doped, n-type had electrons as majority carrier so n-type material is used doped and the intermediate layer that is the intrinsic region has no free, they are highly resistive that means ‘I’ layer opposes the flow of current.
When we start explaining the working, first of all, we need to categorize the working into two that is forward biased and reverse biased condition as same as p-n junction diode.
Pin diode Unbiased condition
- At unbiased conditions, P-I junction and N-I junctions are formed also called depletion layer, due to the high resistive property of the intrinsic layer.
- And even at the intrinsic layer, the electron and holes are present.
Pin diode forward bias
- At the time when the power supply is connected in forwarding condition, the width of the depletion layers at both the junction will decrease eventually.
- And the electrons at the intrinsic layer flows towards the p-type layer and also hole flows towards the n-type layer
- After that, a current is start flowing from p- layer to n-layer
- The pin diode simply works as a variable resistor at forwarding conditions.
- That means at the time when forward voltage increases, the resistance of the intrinsic layer decreases and vice versa.
Pin diode reverse bias
- When we connect the pin diode in reverse biased condition
- The width of the depletion layers such as the P-I junction and N-I junction will increase dramatically.
- At the same time, electrons-holes charged carriers at the intrinsic layer combine each other and disappear.
- And when we further increase the reverse voltage, the depletion region almost covers the whole intrinsic layer.
- This particular voltage is called swept-out voltage.
- In a reverse voltage condition, the pin diode works as a variable capacitor
- The width of the intrinsic semiconductor layer is inversely proportional to the capacitance of the device.
characteristics of pin diode
- The forward characteristics graphically indicated that X-axis is the forward current and Y-axis is resistance.
- At the initial stage resistance value is at its higher position and eventually with an increase in voltage, the resistance inversely proportional to current flow.
- At the reverse characteristics, the X-axis indicates the reverse voltage and Y-axis indicates diode capacitance.
- On the starting stage capacitance of the diode is at its peak, but after reverse voltage increases, the capacitance value drops to a constant value.
Application of Pin diode
When we consider the applications of Pin diode, most of the applications are dependent on reverse-biased conditions, but as an electronic component, every component has its purpose at the time they build. In this category, we list very important applications of pin diode.
At normal conditions a pin diode acts as a rectifier at low frequency also called microwave frequency, the pin diode just behaves like a resistor.
That resistance value is determined by the level of DC that is present at the intrinsic layer.
Higher frequency applications
The Pin diode is known as the DC-controlled high-frequency resistor, if no current is present the diode behaves like an open circuit.
The higher frequency circuit works with an important concept that is, at reverse biased condition capacitance of diode decrease due to increased width of the intrinsic layer.
F = 1/ 2π*XC C
Applying this formula capacitance is inversely proportional to frequency, which means higher frequency signals will be applicable on pin diode.
At the pin diode, the width of the intrinsic layer is higher, the photodetection property of the pin diode is possible.
When the light falls at the depletion region, the covalent bonds at the region will break, then the charge carriers generated and current may flow through the region, so pin diode is a type of photodetector, used to convert the optical signal into an electrical signal.
The amount of space for photo-sensitive applications is higher at the intrinsic depletion layer.
The RF switch is one of the main applications of the Pin diode, a larger combination of components is used to build an RF switch, but this is the main of the whole circuit.
We know photodiode covers the RF signal range, so utilizing the frequency property of the Pin diode at the RF switches.
The Pin diode can also use to build limiter circuits, we know limiters are the passive device that has a low loss for small signals.
The limiters are just like clipper or clamper circuits, application-wise they are used to restrict or allow a different range of signals to the device.
This is just a simple application of limiter circuit, other than this limiter had enormous applications at communication devices.
Advantages of Pin diode
- Highly sensitive to light
- Linear operation
- Wide range of frequency response
- Less expensive
- Low noise
- Low dark current
- Higher reverse voltage to be tolerated
- High-speed response
- Low junction temperature
- Larger depletion region
- Lower capacitance
- High-frequency applications
Disadvantages of Pin diode
- Less sensitivity
- No internal gain
- High reverse recovery time
- Small active area
- Temperatures depended
- Poor temperature stability
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