Simulation Study Of Photodetectors Based On Photodiode And Phototransistor

In this paper,the photodetector based on compound semiconductor has been studied intensively.Using Silvaco TCAD,the PIN photodiode(PD),pnp InGaAs/InP heterojunction phototransistor(HPT)and npn InGaN/GaN HPT are modeled based on practical devices.Firstly,by adjusting device and model parameter,the experimental current-voltage and photoresponse curves are in good agreement with simulated results.This can help us have a better understand of the device working principle and ensure the reliability of the simulated results.Then,optimize the device structure.In order to improve the photoresponse and reduce the dark current,the doping concentration,thickness and material of different layers for PIN PD infrared(IR)photodetector,pnp InGaAs/InP HPT IR photodetector and npn InGaN/GaN HPT ultraviolet(UV)photodetector are optimized.To obtain the best output characteristic and optimal structure,the signal to noise ratio(S/N)and photoresponse are simulated and contrasted.The energy band diagrams and electric field maps for different device structure are also simulated.Finally,the conclusions are obtained after simulation and theoretical analysis: 1)Increasing the doping concentration of absorption layer of PIN PD can reduce the dark current of the detector,and the photoresponse would not be much affected;increasing the thickness of absorption layer can enhance light absorption,and the dark current almost doesn't increase;increasing the reverse bias voltage can reduce the response time of the detector.2)Increasing the doping concentration of subcollector of pnp InGaAs/InP HPT can enhance the electric field in collector to base junction,which is conducive to the collection of holes and the separation of photogenerated electron-hole pairs;lowering the base doping concentration can reduce the the injection barrier height of holes;decreasing the base thickness can reduce hole recombination rate in base region,so holes reach to the collector region more easily;the intrinsic layer has the function of reducing dark current due to the increase of electron barrier between emitter and base,which can block electron impurity injection from emitter to base;the gradient of In composition in base can not only reduce the hole injection barrier,but also change the structure of the valence band,which has conducive to the holes diffusion into the collector.3)For the npn InGaN/GaN HPT,when the material of the collector is GaN or the doping concentration of collector increases,the height of electronic barrier decreases and the electric field in base to collector junction increases,resulting in the reducing of avalanche breakdown voltage;when the doping concentration of the intrinsic layer between base and collector is low,the performance will be improved under low bias voltage.