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.