Progress in MOCVD growth of HgCdTe heterostructures for uncooled infrared photodetectors

摘要

This paper describes the significant progress in the development of metalorganic chemical vapour deposition of Hg_(1-x)Cd_xTe (HgCdTe) multilayer heterostructures on GaAs/CdTe substrates for uncooled infrared photodetectors. The paper focuses on the inter-diffused multilayer process (IMP). The optimum conditions for the growth of single layers and complex multilayer heterostructures have been established. One of the crucial stages of HgCdTe epitaxy is CdTe nucleation on GaAs substrate. Successful composite substrates have been obtained with suitable substrate preparation, liner and susceptor treatment, proper control of background fluxes and appropriate nucleation conditions. Epiready (100) GaAs wafers with 2-4° disorientation towards < 100 > and < 110 > have been used. Due to the large mismatch between GaAs and CdTe, both (100) and (111) growth may occur. Generally, layers with orientation (100) show superior morphology compared to (111), but they are also characterized by hillocks. The benefits of the precursors, ethyl iodine (EI) and arsine (AsH_3), for controlled iodine donor doping and arsenic acceptor doping at dopant concentrations relevant for HgCdTe junction devices are summarized. In situ anneal seems to be sufficient for iodine doping at any required level. In contrast, efficient As doping with near 100% activation requires ex situ anneal at near saturated mercury vapours. Finally, the multilayer fully doped heterostructures for photovoltaic devices operated at room temperature have been fabricated. The special attention is focused on the improvement in multijunction LWIR photovoltaic detectors. The performance of photodiodes is also presented.