This paper describes comprehensive analytical and simulation models for the design and optimization of the electron-injection based detectors. The electron-injection detectors evaluated here operate in the shortwave infrared range and utilize a type-II band alignment in InP/GaAsSb/ InGaAs material system. The unique geometry of detectors along with an inherent negativefeedback mechanism in the device allows for achieving high internal avalanche-free amplifications without any excess noise. Physics-based closed-form analytical models are derived for the detector rise time and dark current. Our optical gain model takes into account the drop in the optical gain at high optical power levels. Furthermore, numerical simulation studies of the electrical characteristics of the device show good agreement with our analytical models as well experimental data. Performance comparison between devices with different injector sizes shows that enhancement in the gain and speed is anticipated by reducing the injector size. Sensitivity analysis for the key detector parameters shows the relative importance of each parameter. The results of this study may provide useful information and guidelines for development of future electron-injection based detectors as well as other heterojunction photodetectors. V
Recent results from our electron-injection detectors as well as other heterojunction phototransistors with gain suggest that these devices are useful in many applications including medical imaging, light detection and ranging, and low-light level imaging. However, there are many parameters to optimize such structures. Earlier, we showed a good agreement between experimental results and our models. In this paper, we provide detailed analytical models for rise time, gain, and dark current that very accurately evaluate key parameters of the device. These show an excellent agreement with detailed three-dimensional numerical simulations. We also explore a figure of merit that is useful for low-light-detection applications. Based on this figure of merit, we examine the ultimate sensitivity of the device. Furthermore, we explore the effects of variations in some of the key parameters in the device design and present an optimum structure for the best figure of merit. Our models suggest ways to improve the existing devices that we have, and may be a guideline for similar phototransistors.
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