PAC and XPS studies of II–VI compounds

Abstract

The perturbed angular correlation (PAC) method has considerable potential for studying near-surface defects of materials on a microscopic scale, especially in combination with standard surface techniques. We have characterized the near-surface and surface regions of II–VI compounds using PAC and X-ray photoelectron spectroscopy (XPS). PAC was used to identify point defect complexes containing the radioactive 111In probe atoms, which were diffused into Cd 0.96Zn 0.04Te, Cd 0.8Mn 0.2Te and Hg 0.79Cd 0.21Te (MCT) samples under vacuum from 200 to 550 °C. After the Cd(Zn)Te samples were annealed at 450 °C for 30 min, 60% of the In atoms occupied unique non-cubic sites, characterized by an interaction frequency ν Q = 60 MHz and an asymmetry parameter η=0.2. These sites were attributed to In-(cadmium vacancy) complexes, since this signal was eliminated by subsequent annealing in a cadmium atmosphere. Similar results were obtained for the Cd(Mn)Te samples, but the vacancy complex occured at a lower annealing temperature. The XPS data for Cd(Mn)Te showed that its oxide characteristics differed considerably from those of CdTe. Although oxide formation of CdTe occurs very slowly after sputter cleaning, a significant TeO layer was formed on the Cd(Mn)Te surfaces after only 10 min exposure to air. In addition, deionized water removed the native oxide completely for CdTe but not for Cd(Mn)Te. For MCT, annealing at 350 °C caused the formation of two defect complexes, characterized by frequencies of 83 and 92 MHz, and η ≈ 0.1. These PAC signals vanished after annealing under a mercury atmosphere, indicating that they were also due to In-vacancy complexes.