Growth and properties of MOCVD HgCdTe epilayers on GaAs substrates

Abstract

Growth of MOCVD Hg1xCdxTe (HgCdTe) epilayers on GaAs substrates is described. The paper focuses on the interdiffused multilayer process (IMP). In this process, the CdTe/HgTe growth times are comparable with transition times between the phases. The non-optimum flow velocities and partial pressures that may induce poor morphology and reduce growth rate characterize the growth during transition stages. 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 ap-propriate nucleation conditions. Due to the large mismatch between GaAs and CdTe, both (100) and (111) growth may occur. It mostly depends on substrate disorientation and preparation, nucleation conditions and growth temperature. Cd or Te sub-strate treatment just before growth results in (100) and (111) orientation, respectively. 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 (AsH3) for controlled iodine donor doping and arsenic acceptor doping are summarized. Suitable growth conditions and post growth anneal is essential for stable and reproducible doping. 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.