Temperature Dependence of the Defect States in LWIR (100) and (111)B HgCdTe Epilayers for IR HOT Detectors

HgCdTe epilayers grown by chemical vapor deposition (MOCVD) on GaAs substrates operating in the long-wave infrared range were characterized by the photoluminescence (PL) method. Photodiode and photoconductor designs, both (100) and (111)B crystallographic, were analyzed. Spectral current responsivity ( R I ) and a PL signal approximated by a theoretical expression being the product of the density of states and the Fermi–Dirac distribution were used to determine the fundamental transition (energy gap, E g ). For all the samples, an additional deep-level-related transition associated with mercury vacancies (V Hg ) were observed. The energy distance of about 80 meV above the valence band edge was observed for all the samples. Moreover, measurements at low temperature showed shallow acceptor-level (As Te and V H g as acceptors) transitions. In HgCdTe(100), due to the higher arsenic activation, As Te was the dominant acceptor dopant, while, in HgCdTe(111)B, the main acceptor level was formed by the neutral V Hg . The determined activation energies for As Te and V H g dopants were of about 5 meV and 10 meV, respectively.