What are Pin Diodes and Their Operational Characteristics?

Diodes are common to numerous electrical devices, and the PIN diode in particular is a variation of the PN-junction that may benefit various applications. As an advancement over conventional PN-junction diodes, the PIN diode comes in the form of a 3-layer device where an intrinsic layer is situated between P and N regions. The intrinsic region of the diode allows for the component to feature high properties of resistance, coupled with a large electric field. As a result, the electronic and hole pair generation of the region is increased so that a weak input signal may be operated.

PIN diodes are a type of photo detector, utilizing their semiconductor intrinsic region to transform light energy into an electrical form. With their high level of resistance, PIN diodes exhibit a low value of capacitance. The P region of the PIN diode may be created by doping a trivalent impurity to the semiconductor, and the N region is established through the doping of a pentavalent impurity. The intrinsic region, meanwhile, is simply an undoped semiconductor material.

PIN diodes may be manufactured through two methods, those of which follow the planar or mesa structure. The planar structure is where a thin epitaxial layer is imposed on the intrinsic region, allowing for a P+ region to be established. Meanwhile, an N+ region is formed on the opposite side of the device, allowing for the intrinsic region to exhibit a high resistance with a value around 0.1 Ω-m. Mesa structures, meanwhile, are where the doped semiconductor layers are developed on the intrinsic region. By following such a method, a PIN diode is formed.

As compared to conventional PN junction diodes, PIN diodes mostly differ in the presence of their intrinsic region. Generally, the intrinsic region acts as a depletion region. In situations where there is no external potential provided to the diode, carriers will begin to diffuse across the junction as a result of the concentration gradient. Because of this, a depletion region is formed where the I region exhibits higher thickness than the N region.

When a forward voltage is induced to the diode, the charge carriers from the P and N region will be injected into the intrinsic region. This is a result of the applied forward potential reducing depletion width, causing the resistance to lower. With further increases of forward voltage, a greater number of charge carriers would be injected into the intrinsic region. Due to such capabilities, PIN diodes in forward biased condition may act as a variable resistance device.

Reverse bias voltage may also be induced to the PIN diode, resulting in an increase of depletion width. To increase the width further, the reverse voltage may be raised. This increase can continue as whole mobile carriers are transferred away from the intrinsic region to create what is known as swept out voltage. When in a reversed biased condition, the PIN diode may act as a capacitor.

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April 8, 2021
March 29, 2021

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