Electrical properties of CdTe films prepared by close-spaced sublimation with screen-printed source layers

Abstract

CdTe films have been deposited by a close-spaced sublimation process with screen-printed CdTe layers as a new source. The source-layers were fabricated by screen printing and sintering slurries consisting of propylene glycol, CdCl2 and either CdTe powder or (Cd+Te) powder. When CdTe powder was used as a starting material for the source-layer, the electrical resistivity of the CdTe film deposited in O2 was about one-tenth lower than that of the film deposited in He. AES, EDS and PIXE analysis showed that the Cd content in the CdTe films deposited in O2 was smaller than that in the CdTe films deposited in He. Especially, no oxygen element was detected in the CdTe films deposited in O2. It turned out that the sublimated Cd(g) and CdTe(g) from the source-layer formed cadmium oxides in O2 and as a result the overall composition of vapor source became more Cd-deficient. The CdTe film with less Cd content increased cadmium vacancy defects (VCd2−Cl+ and VCd2−) and hole concentrations. As the Cd/Te ratio in the starting (Cd+Te) powder decreased, the resistivity of the CdTe films decreased and reached at a constant value of about 3x104 Ω⋅cm, regardless of deposition atmosphere. In addition, the resistivity decrease by O2 treatment was diminished when the Cd/Te ratio was below 0.7, where the composition of CdTe film might be limited by solid solubility (Cd0.92Te1.0). The above results indicated that the resistivity decrease of CdTe films deposited in O2 was not due to the effect of previously-known oxygen doping but due to the effect of Cd/Te compositional change.