Luminescence characterization of residual impurities in CdTe grown by molecular beam epitaxy

Abstract

The optical properties of CdTe grown by molecular beam epitaxy (MBE) on 〈100〉 InSb substrates have been studied by high resolution photoluminescence and resonant excitation spectroscopy. The layer thickness varied between 2 and 8 μm and the substrate temperature during deposition was in the range of 150 to 300°C. Sharp and strong lines associated with impurity bound exciton recombination are observed and indicate a good crystalline quality as well as a low level of impurity contamination. From a close comparison with the luminescence spectra obtained on bulk material, the acceptor impurities Cu, Li (or Na) and Ag have been unambiguously identified in MBE grown CdTe. Two-electron transitions have also been detected by resonant excitation of the donor bound exciton lines and associated with In and Cl impurities. The appearance of a double band near 1.55 eV is attributed to (D,A) recombination with pairing effects. The relatively high concentration of indium results probably in this case from a contamination by the substrate.