New insight into defect energy levels in HgCdTe

Abstract

The paper reports on a summary of the experimental data on the defect energy levels in HgCdTe, that have been collected in our experiments and from articles available over several decades. We have determined the location of the defect levels in HgCdTe for material composition from 0.17 to 0.6. It has been shown that that all specified trap levels are tied to the valence band and do not change (or change slightly) with temperature, and have the slopes with respect to the Cd molar content somewhat smaller than the HgCdTe energy gap.Two levels are formed by mercury vacancies – the first defect level is a shallow acceptor formed by neutral vacancy, the second deep level can be formed by singly negatively charged Hg vacancy. Contrary to earlier assumptions, it does not lie in the middle of the energy gap for the entire range of molar composition, but it is an acceptor-like for the wide-gap HgCdTe and a donor-like for the narrow gap, and may even be located in the conduction band forming a resonant state. Above this main defect level, two additional trap states can be found, most likely formed by oxygen atoms replacing Hg vacancies – positively charged and the neutral oxygen states.