Unique deep levels in spectroscopic CdZnTe: Compensation, trapping, and polarization

摘要

-0.7 eV. We characterized the defects in several ways, including measuring the photoconductivity at below-bandgap excitation, and photoconductivity quenching by comparing their positions in the bandgap with that of the native energy-levels in CdTe quantum dots (QDs) and other II-VI semiconductors. In this way, we determined unambiguously that a deep acceptor, Cd vacancy, behaves as a doubly charged acceptor, and the second ionization level is located at ∼ EV+(0.5±0.05) eV, i.e., far from the mid-gap. This configuration may determine the lifetime of holes, but it does not stabilize precisely the compensation condition, and it is not responsible for electron trapping and polarization. We demonstrated that a self-consistent model of compensation, electron trapping, and polarization should be based on a doubly charged donor (D) with two electrical states D(2+/1+) and D(1+/0), one of which is located close to the mid-gap and is separated from the second by a potential barrier that prevents fast trapping of the photoelectrons from the conduction band, but can be responsible for polarization.