Study On The Mechanism Of Photoelectric Response Characteristics For Hgcdte Infrared Detectors

Mecury cadmium telluride (HgCdTe) infrared photodetectors are widely used in advanced infrared detector systems operating in1-3,3-5and8-12μm atmospheric windows. With the development of the HgCdTe infrared detector technology in recent50years, the material of HgCdTe is almost on the similar position in infrared technology field as Si in microelectronics. However, current property of HgCdTe can hardly meet the demand in civilian and military fields. Since fabrications of HgCdTe devices are very complicated and expensive, device simulation has become a critical tool for the development of HgCdTe devices. Device simulation can reveal the physical limits of device performance and provide information for further improvement. Not only does it reduce the research cost, but it also provide a practical applicable and time-and labor-saving means for improving the device quality, reliability and performance for the device optimizations. Device simulation has become one of important steps in design and fabrication of HgCdTe devices.The emphasis of this dissertation is the establishment of the applicable numerical model and analytic model for HgCdTe device simulations, and using them in the analyzing, optimization and design of HgCdTe photodectectors. The main contents are given as follows:1. Modeling of the highly doped HgCdTe infrared photodiode. The photo-response blueshift of the n-type conversion region for HgCdTe infrared photodiode is numerically investigated. The following three contributions are considered:(i) the Burstein-Moss (BM) shift considering a nonparabolic conduction band,(ii) the band gap narrowing (BGN) effect, and (iii) the Hg-vacancy-induced acceptor trap level. It has been shown that the photoresponse curve of the n-type conversion region shifts remarkably toward high energy than p region. The result can be used to explain quantitatively the recent experimental observation of the blueshift of the photoluminescence peak for the n-type conversion region. It is concluded that the BGN and nonparabolic effects play an important role in the photoresponse of n+-on-p HgCdTe infrared photodiode with heavy doping concentration.2. Different carrier statistics approximations for the performance analysis of infrared HgCdTe devices. Comparing the calculated results to the experiments, we get the most accurate model of HgCdTe carrier statistic approximation. Three different carrier statistics approximations:(i) parabolic conduction-band approximation,(ii) Bebb’s nonparabolic expression, and (iii) Harman’s nonparabolic approximation, are proposed to calculate the optical bandgap and photoresponse of HgCdTe photovoltaic devices by considering the carrier degeneracy and the nonparabolic conduction band. It is found that omitting nonparabolic effect can lead to an enormous deviation in the simulation result, especially for heavily doped HgCdTe devices. On the basis of the calculated results of photoresponse, the parabolic conduction band and Harman’s nonparabolic approximations can lead to the photoresponse peak shift to short and long wavelengths, respectively.3. Establish the transport model of amorphous HgCdTe (a-MCT) infrared detector. Temperature dependence of dark current and photo current are investigated for a-MCT infrared detector at80-300K. The maximal value of detectivity is formed at above200K. It is indicated that an uncooled a-MCT infrared detector may be fabricated based on the Si-based a-MCT. Based on Mott and Davis carriers transport model, we point out that the transport transition between the localized and extended state leads to the maximal Iph/Id at about210K.4. Based on the dark current characteristics of infrared photovoltaic detectors, a simultaneous mode nonlinear curve fitting approach is used to analysis the dark current mechanisms of long-wavelength arsenic doped HgCdTe infrared photovoltaic detector at various temperatures. Using this method, the dark current mechanisms of devices can be analyzed, and devices parameters can be extracted. This method has been used to fit the R-V curves of arsenic doped HgCdTe infrared photovoltaic devices at different temperatures. The dependence of devices parameters on temperature have been obtained, and get the main restriction physical mechanism for improving the performance of long-wavelength arsenic doped HgCdTe infrared photovoltaic devices. Study on the dark current suppression effect of unipolar barrier infrared detectors. Numerical simulation was used to calculate the current-voltage (Ⅰ-Ⅴ) characteristics and R0A values for unipolar barrier photodiodes and traditional pn junction photodiodes. Furthermore, the physical mechanisms of several dark current components of the unipolar barrier structure have been investigated. Comparing to conventional devices, the unipolar barrier device has shown significant performance improvements.