Effect of heat treatment on p-type CdTe crystals and CdS/CdTe heterojunctions formed by chemical vapor deposition

Heat treatment of p‐type CdTe:P single‐crystal wafers in hydrogen at temperatures between 310 and 475 °C decreases the hole density near the CdTe surface by as much as a factor of 25, and produces an approximately exponential acceptor density profile. Deposition of CdS during the heat treatment prevents most of the decrease in hole density, presumably by acting as a diffusion barrier against diffusing impurities. CdS/CdTe solar cells prepared by chemical vapor deposition of CdS on CdTe single crystals show efficiencies in the 8 to 10% range. Junction capacitance analysis suggests that the bands are bent strongly toward the Fermi level at the surface, with diffusion potential approximately equal to those expected from a simple junction model.