MECHANICAL-PROPERTIES OF CDTE

Thermal and mechanical stresses are thought to play an important part in the formation and multiplication of dislocations during the directional solidification of CdTe. To evaluate the effects of stress on crystal quality, it is necessary to know the mechanical properties of CdTe at all temperatures that a growing ingot would experience. In this context, we have determined the stress-strain behavior and the critical resolved shear stress (CRSS) of CdTe from 300 to 1353 K. Single crystal CdTe specimens, oriented along the (132) axis, were uniaxially compressed at a strain rate of 10(-4) s-1 at different temperatures. B2O3 was used as an encapsulant to prevent evaporation of CdTe at temperatures of 773 K or above. The CRSS decreased rapidly with increasing temperature up to 400 K, was nearly constant between 400 and 800 K, and decreased again beyond 800 K. The CRSS ranged from 5 MPa at 300 K to about 0.2 MPa at 1353 K. The shear modulus ranged from approximately 100 MPa at 300 K to 30 MPa at 1353 K. B2O3 did not appear to affect the onset of plastic deformation. The apparent shear modulus values were lower with the use of B2O3. In a related work, we studied in situ the effect of applied stress on tensile specimens of Si, Si-doped GaAs and CdTe crystals by synchrotron X-ray topography. Results indicate that defects, believed to be dislocations, began to move and multiply in Si-doped GaAs and Si crystals at stresses that were approximately 0.3 to 0.6 times the CRSS calculated from an engineering stress-strain diagram. Dislocation motion could not be observed in CdTe due to the poor resolution of the topographs of CdTe samples.