PIN diode AND it's Application
PIN diode
A PIN diode Is basically a photo detector used to convert optical signal into an electrical signal. It consist of three region called P-region, an intrinsic region and N-region.
It's working principle is almost same as that of normal PN diode. The main difference is the depletion region which exist in junction region of PN diode. Here in this diode depletion layer exist completely in intrinsic region. This depletion region is much better than in PN diode and nearly constant size independent of reverse biased applied to the PN diode.
The p-region in PIN diode contains holes as majority career and N region contains electron as majority career. The intrinsic region between p type and n-type semiconductor now flooded with access of equal number of electron and holes.
Under forward biasing to PIN diode the width of depletion layer decreases the injected career concentration is typically several order of magnitude higher than the intrinsic carrier concentration. As a result the electric field extend deeply into the region. This electric field assist in a speeding up of the moving charge carrier from P to N region which result in faster operation of diode, making it suitable device for high frequency operation. Thus in forward biasing it act as a variable register by providing variable resistance and in reverse biased it provide infinite resistance and thus act as a perfect switch.
Under forward biasing to PIN diode holes and electrons are generated from p and n region into I region and these charge carrier do not recombine immediately rather a finite quantity of charge always remains stored and result in lowering of the resistivity of I region the quantity of store charge q depends on the recombination time t and forward bias current I.
Q=IT
The resistance of I vision under forward bias rs is inversely proposal to q and maybe expressed as...
Rs= W^2/( μp+μn)Q
Where w is with of intrinsic reason μp and μn are respectively holes mobility and electron mobility combining above equation we have.....
Rs= W^2/(( μp+μn)/t)
When PIN is at zero or reverse bias it appears as a parallel plate capacitor having a value of capacitor as.....
C = εΑ/W
Where ε is dielectric constant of semiconducting material. A is the junction area and W is the width of intrinsic region at low reverse voltage is increased careers are depleted from I region resulting in an essentially loseless capacitor and thus can be used as switch.
Application of PIN diode
High Voltage rectifier
PIN diode is used as high voltage rectifier. The large width of intrinsic layer makes it to tolerate high reverse voltage without leading to the breakdown of the diode.
Radio frequency switch
Under reverse biasing pin diode can be used as rectifier and microwave switch. The width of intrinsic layer is comparatively more than layers of semiconductor, thus more the with more will be the separation between semiconductor layer and the less will be the capacitance.
Photo diode
Since the conversion of electric current into the light is possible in intrinsic region of pin diode so more the width of intrinsic region more will be the efficiency of the diode for generating light thus pin diode can be used as photo diode.
Attenuator
Under forward biasing PN diode works as a variable register therefore it can be used for protection of rectifier circuit from high current when the forward biasing is increased the resistance of diode decreases so it can be used as attenuator.
