Photoplastic Behavior of CdTe

Abstract

Single crystals of CdTe have been grown by the Bridgman technique with boric oxide as liquid encapsulation. The nonstoichiometry of these p‐type crystals was changed by heat treating in Cd vapor of different partial pressures. Mechanical measurements performed in compression on the n‐ and p‐type crystals in darkness and during illumination showed that high‐resistivity crystals had the lowest yield stress; at the same time, only a very small influence of illumination on the yield stress could be detected. The yield stress of low‐resistivity samples, however, could be increased as much as 70% by illumination with light corresponding to the band‐gap energy. Strain‐rate cycling tests have been performed in compression on as‐grown crystals. The Johnson‐Gilman velocity‐stress relationship was used to evaluate the dislocation velocity effective stress exponent and the long‐range internal stresses built up during deformation in light and darkness, respectively. The observed increase in flow stress during illumination is consistent with a semiphenomenological model, which assumes a light‐induced decrease in the mobile dislocation density by pinning of charged dislocations by oppositely charged native defects.