The exciton and edge emissions in CdTe crystals

A detailed analysis of photoluminescence (PL) spectra of solution grown CdTe samples with and without thermal annealing were investigated to ascertain the nature of exciton and edge emissions in the CdTe crystals. The temperature dependence of emission line intensities was also studied. In both as-grown and Te annealed CdTe samples, among other peaks, a sharp acceptor-bound exciton (AoX) line at 1.589 eV was observed. By Cd annealing, the AoX and the edge emission lines simultaneously disappeared while the intensity of a donor-bound exciton (DoX) line was increased. The experimental results suggest that the AoX line in the as-grown sample is due to excitons trapped at the complexes, each formed with a Cd-vacancy and two unidentified donors (VCd-2D). In the Te annealed samples, we observed overlapping of edge emissions, which result from two different acceptors. In addition, the intensity of the AoX line at 1.589 eV was obviously enhanced by the Te annealing. From these results, it may be concluded that the AoX line in the Te annealed samples is due to two origins, related to VCd-2D and an acceptor-like structural defect. The acceptor-like structural defect can be assigned to Cd-vacancy (VCd). The ionization energies of VCd-2D and VCd are about 56.4 and 50.4 meV, respectively.