Research On Semiconductor Detectors Irradiated By In-band And Out-of-band Laser Beams

With the widespread use of photoelectric detectors in different domains, especially in military, more and more attentions are being paid to the irradiation effects of semiconductor materials and photoelectric detectors. The spectrum of the photoelectric detectors ranges from ultraviolet to far-infrared since there are plenty of semiconductor materials. However, as far as a specific detector is concerned, it can only responses to a specific band. We call the lights within the band"in-band lights"; otherwise we call them"out-of-band lights". The scientific society knows well the irradiation effects of detectors by in-band lights, while there is little knowledge of the corresponding effects by out-of-band lights, which is also important in photoelectric countermeasure.This dissertation is focused on the mechanism of the interaction between in-band and out-of-band lasers and photoelectric semiconductor detectors via theoretical and experimental researches. Exploratory research is also made on the interference and efficient damage of out-of-band lasers on photodetectors.We carried out plenty of experiments in which different types of photoconductive (PC) detectors were irradiated by out-of-band lasers, finding that the voltage responses of detectors irradiated by out-of-band lasers were opposite to those by in-band lasers. We also studied the output of the detectors when irradiated by both in-band and out-of-band laser beams. Basing on the experimental results, we find the relationship between the output and the laser intensity. We conclude that a) there also exists saturation effect for the voltage response of PC detectors when irradiated by out-of-band lasers, b) in-band laser irradiation can increase the absorption of the out-of-band lasers, and c) in-band laser irradiation within linear-response domain can enhance the response of out-of-band lasers.We carried out experiments on photovoltage (PV) detectors irradiated by out-of-band lasers, and get the ruls of dynamic responses. We find that the voltage response of PV-type detector to out-of-band lasers is similar to that to in-band laser, while there were instantaneous jump for the voltage both at the beginning and at the end of laser irradiation. The direction of the voltage jump varied with laser intensity. Analysing the physical progress, we find new mechanics of voltage response, which we call thermovoltage. Comparing with photovoltage and thermopower, thermovoltage is the main mechanics of voltage response when out-of-band laser irradiating,and thermovoltage combines with photovoltage, thermopower and Dember voltage when in-band laser irradiating.Using double integrating sphere-photo detector system, we measured reflectance and transmittance for semiconductor materials under irradiation of both in-band and out-of-band lasers, getting the energy-coupling rules of semiconductor materials and lasers. We find that a) the energy-coupling coefficient of materials with in-band lasers decreases with in-band-laser power density increase; b) the coefficient for out-of-band lasers increases first and diminishes subsequently when the out-of-band laser power density increase; and c) irradiation of in-band lasers can increase the coupling coefficient for the out-of-band lasers.To explain the abnormal response of the PC-type detector for out-of-band lasers, we bring forward a concept of photoexcited hot carriers transportation. Basing on Boltzman formula, we obtain the energy balance hydrodynamic model under third-order approximation, which can describe the transportation of pohtoexcited hot carriers. Accordingly, we made a procedure that can describe different cases. Simulations for a PC-type HgCdTe detector irradiated by in-band and out-of-band lasers were done, agreeing well with experimental results. Basing on the procedure, we also have got the destruction threshold of detectors under different irradiating time and power.