Depth profiling sulphur in bulk CdTe and CdTe/CdS thin film heterojunctions

Polycrystalline CdTe-CdS heterojunction solar cells are a possible candidate for the low cost, high efficiency conversion of solar energy. The formation of an intermediate CdSxTe1-x layer during a high temperature annealing stage is believed to increase optical absorption and decrease cell efficiency. S diffusion in single crystal CdTe has been investigated by NRA using the S-32 (d,p(0)) S-33 nuclear reaction, at a deuteron energy of 2 MeV. Details of the NRA depth profiling procedure are given, which was found to be relatively straightforward and suitable for use on a small Van de Graaff accelerator. The resulting diffusion parameters are compared to those obtained by SIMS using a Cs+ primary ion beam, examining negative secondary ions. The diffusion coefficients were found to be 1.1 x 10(-15) cm(2) s(-1) at 450 degrees C and similar to 8 x 10(-15) cm(-1) s at 550 degrees C. S diffusion in thin films was also investigated by 2 MeV He-4(+) RBS on annealed polycrystalline CdS-CdTe multilayers. (C) 1998 Elsevier Science B.V.