Research On Long Pulse Laser Damaging On Silicon APD Photodetector

The photoelectric conversion,photothermal conversion,thermal stress and other phenomena will be appeared when the silicon based APD(Si-APD)detector is irradiated by the long pulse laser,and the damage process is very complex.In this paper,the damage process,the effect and the law of the long pulse laser irradiated Si-APD are studied by the methods of theory,simulation and experiment,the relationship between the laser parameters and the damage effect is analyzed,and the damage law and mechanism of the long pulse laser irradiated Si-APD are expounded.A theoretical model of electrical,thermal and thermal stress for the long pulse laser irradiated Si-APD is established.In the electrical theoretical model of Si-APD irradiated by long pulsed laser,the semiconductor model,dark current density model,multiplication factor model and output current model are built,respectively,and which can descript of the electric field(depletion layer length),optical current density,recombination rate,dark current density,multiplier factor,output current.In these models,the output current model can be divided into the output current model of the photocurrent phase,the conduction phase and the recovery phase;The theoretical model for thermal and thermal stress of Si-APD detector irradiated by long pulse laser is established based on the energy conservation equation,the traditional heat conduction equation and the thermoelastic basic equation,the combined effects of laser heat,Joule heat and compound heat are considered in the model,and a reasonable explanation of the "small platform" phenomenon in the temperature rise curve is given.On the basis of the theoretical model,the electrical simulation model,heat and thermal stress simulation model of the long pulse laser irradiated Si-APD are established.By calculating the electrical simulation model,we found that the electric field is increased with the external bias and temperature increasing;The photocurrent density is increased with the temperature and light intensity increasing;The dark current density,multiplication factor are increased with the temperature increasing;When the laser irradiating the Si-APD,the output current is increased rapidly to a peak,after falling to a fixed value,maintain a period of time,down to the original value;In the photo generated current stage,the peak value of output current is increased with the increase of the energy density,and the output current is equal in the conduction stage,and the recovery time is increased with the increase of the laser energy density in the recovery stage.The peak value of the output current and the output current in the conduction phase are increased with the increase of the external bias voltage.By calculating the thermal and thermal stress simulation model,we found that the temperature of the center point of the upper surface is increased with the increase of the irradiation time,when the value is increased to a certain value,the temperature rise speed is slowed down;Under the condition of the same energy density,the temperature rise speed is slowed with the increase of pulse width,and the highest temperature is decreased with the increase of pulse width;The temperature rise speed and the maximum temperature are increased significantly with the energy density under the same pulse width;When the external bias increases to 90 V,the Joule heat begins to produce,causing the temperature of the central point at the PN junction to increase quickly to a peak,then decline,and then increase slowly;The temperature of the central point at the PN junction increases with the increase of the energy density under the same external bias;The radial thermal pressure is the cause of the initiation of interlayer splitting.The temperature measurement system,output current measurement system,damage area measurement system and electrical parameter offline measurement system of Si-APD detector irradiated by long pulse laser are constructed.The temperature rise time and damage area of the center point are increased with the increase of pulse energy density and are decreased with the increase of pulse width in the experimental study;The peak value of the output current is increased with the increase of the energy density,and the peak time of arrival is basically the same;The response and multiplication factor are decreased with the increase of pulse energy density,and the dark current is increased with the increase of pulse energy density,and the C(V)cures show that the decrease of junction capacitance caused by avalanche layer.The comparison between the experimental and simulation results show that the laws of the two research results are basically the same,and the simulation model can reasonably describe the process of long pulsed laser irradiation of Si-APD.The damage mechanism of Si-APD irradiated by the long pulse laser is given in combination with the results of damage morphology,temperature and output current.