Studies on carrier-blocking structures for up-conversion infrared photodetectors

Abstract

Infrared (IR) photodetectors have been widely used in the fields of both civil and military applications such as environmental monitoring, medical diagnostics, satellite remote sensing and missile guidance, etc. In conventional large scale focal plane array (FPA) IR imaging, the thermal mismatch between IR photodetectors and silicon readout circuits will inevitably lead to the degradation of the device performance. An up-conversion IR photodetector, which converts IR photons to short-wavelength photons for Si-CCD-based imaging, can avoid thermal mismatch caused by hybridization with silicon readout circuits, resulting in a low-cost way for large array IR imaging. The operation principle of the semiconductor up-conversion IR photodetector is based on electron transitions and carrier transportation in different functional sections including absorption section, transportation section and emission section, hence the carrier distribution in the device structure has a crucial influence on the device performance. In order to achieve low dark current, carriers are expected to be non-uniformly distributed in the up-conversion device structure. Designing and optimizing the carrier-blocking structure are usually the key issues to acquire inhomogeneous carrier distribution. In this paper, up-conversion infrared photodetectors with various hole-blocking structures are investigated both theoretically and experimentally. Firstly the carrier distributions are calculated by self-consistently solving the Schr?dinger equation, Poisson equation, current continuity equation and carrier rate equation. Then the influence of the carrierblocking structure on the device performance is analyzed by electroluminescence measurements on the corresponding epitaxial structures. According to the theoretical and experimental results, it is found that a 2-nm-thick AlAs barrier layer can block holes effectively without hampering the electron transportation, which is necessary for the up-conversion infrared photodetectors. However, other attempts to block holes, such as light n-doping in the transportation section or lowering the injection barrier, do not work well. In addition, the influences of the thickness and height of the blocking barrier and the operation temperature on the carrier distributions are also studied. When the thickness of the blocking barrier is less than 2 nm, the thicker or the higher is the barrier, the better is the blocking effect. However, when the thickness of the blocking barrier is larger than 2 nm, the blocking effect is not persistently enhanced with increasing thickness because the tunneling process is almost fully suppressed. Furthermore, with the same blocking barrier parameters, lowering the operation temperature can lead to better blocking effect. This work demonstrates the utilization and effect of carrier-blocking structures in semiconductor devices which deamnd an inhomogeneous carrier distribution.