Characterization and annealing behavior of deep levels in CdTe epitaxial layers

Abstract

Deep defect levels play an important role in determining minority carrier lifetimes in CdTe photovoltaic devices. Much work has been done on the investigation of defects in bulk CdTe. In this paper we report on results obtained in CdTe thin epitaxial films, deposited on BaF2 and PbTe by hot-wall epitaxy. Deep Level Transient Spectroscopy was used to measure the energy levels, the capture cross sections, and concentration profiles of the defect levels. The measurements were performed on PbTe/CdTe heterojunctions and Au/n-CdTe Schottky barriers. Six levels were identified in the CdTe layers (E1 = 0.20 eV, E2 = 0.36 eV, E3 = 0.34 eV, E4 = 0.24 eV, E5 = 0.46 eV, E6 = 0.64 eV). By measuring the capture cross section separately an activation energy of 60 meV for the capture cross section of level E3 was found. The concentration of some of the defects could be reduced by annealing.