Cathodoluminescence study of the effect of annealing in HgI_2 vapor on the defect structure of CdTe

Abstract

The origin and spatial distribution of radiative defects in undoped and Ge-doped CdTe wafers have been studied by CL spectroscopy and imaging techniques in the scanning electron microscope (SEM) before and after the wafer annealing in HgI2 vapor. The annealing procedure has been carried out under isothermal conditions at 250 degrees C for 24 h for or for 48 h. It has been shown that the annealing results in the growth of alpha-HgI2 polycrystalline layer on the wafer surface, and this layer acts as a getter for Te precipitates distributed randomly over the whole volume of the as-grown CdTe wafers. The annealing affects mainly the CL bands related with Te vacancies (band at about 1.00 eV) and Ge dopant (0.82 and 0.89 eV bands). The contribution of the latter to the total luminescence emission of CdTe wafers decreases after the annealing. The quality improvement of CdTe wafers, revealed by the elimination of Te precipitates from the wafer bulk, has been shown to be an important result of the annealing procedure.