Impact of an ultra-thin antimony layer on the performance of CdTe-based photodetectors under varying illumination conditions

Abstract

In this study, the impact of thin Sb-layer in the device on CdTe photodetector parameters were examined. CdTe films were deposited by the close spaced sublimation (CSS) method, and then Sb-thin films were grown onto CdTe coated substrates by DC sputtering. In the structural analyses, it was observed that both as-dep and annealed CdTe exhibited the formation of double phases (Cd-rich and Cd-poor CdTe). However, Sb coating on CdTe led to the formation of Cd-rich and stoichiometric cubic CdTe phases. Surface images revealed that all samples exhibited a densely-packed grain morphology, with average grain sizes of 7.74 µm, 8.15 µm, and 7.15 µm for as-dep. CdTe, annealed CdTe, and annealed CdTe/Sb, respectively. It was calculated that the preparation steps of the samples had no considerable effect on the bandgap, as all samples exhibited values within the range of 1.45–1.48 eV. Meanwhile, PL features in the range of 817–820 nm were observed for all samples, attributed to acceptor-bound exciton transitions in the as-dep CdTe, and to donor-bound exciton transitions in the annealed CdTe and CdTe/Sb films. All photodetectors exhibited photoconductive behavior; however, the best performance was achieved by annealing CdTe under Cd-overpressure (R=1.7 mA/W, D*=3.4 ×10⁷ Jones for blue light, and R=2.5 mA/W, D*=5 ×10⁷ Jones for red light). Furthermore, the annealed CdTe photodetector maintained a significant level of performance even after six months without encapsulation. In contrast, Sb coating on CdTe led to a slight degradation in device performance, attributed to its adverse effects on defect levels and grain structure.