Study On Carrier Transportation In Photoelectric Semiconductor Detectors

With the development of photoelectron technology and photoelectric countermeasure technology, it is in our great interest to investigate interaction between laser and photoelectric detectors, especially the dynamic response of detectors under high power laser irradiation. Most of the research work that has been carried out in this field is to measure the damage threshold and to investigate the damage mechanism of various detectors, while the study of carrier transportation and dynamic response of detectors under medium power density laser irradiation (between the saturation threshold and the damage threshold of detector), including chaos in detectors induced by laser, is extremely little. The conventional models are just applicable for low power light irradiation. In this paper, we have carried out systematical research, with both theory and experimental method, on the nonlinear photoelectron transportation and the dynamic responses of detectors under medium power density laser irradiation.A new drift-diffusion model is put forward, with photoconductive effect and heat effect in semiconductor detectors irradiated by high power laser taken into consideration, based on the conventional model. Nonlinear coupled dynamic equations for photoconductive and photovoltaic detectors are established. Imitative calculations to two types of detectors were carried out by using appropriate differential method and designing programs capable of researching their photoelectric character.Experimental researches on the response of photoconductive and photovoltaic HgCdTe detectors under laser irradiation are carried out. New nonlinear phenomena of photovoltaic HgCdTe detectors, that is chaos and zero output, are found for the first time.A new model, called plasma model, describing carrier transportation in semiconductor detectors is proposed, which regards semiconductor materials under laser irradiation as plasma of low temperature and of high carrier concentration. It is our independent innovation to introduce the concept of plasma into photoelectron transport model. The plasma model is programmed to study the response of photoconductive detectors under laser irradiation.The response of photoconductive detectors under out-of-band laser irradiation is analyzed. The response, in our view, is a kind of photoconductive phenomena induced by hot electrons excited by out-of-band laser irradiation. If the power of laser irradiation is high enough to cause notable temperature rise in semiconductor detectors, it will result in the notable change in conductivity.There are innovations in both theoretic study and experimental study presented in our paper. Our models and conventional model give identical results when the detector is under low power laser irradiation. In the case of higher power laser irradiation, our model can be used to estimate the temperature rise of detector material to deduce if the material is to be melted or ablated.