CONSTITUTIVE MODELING FOR CDTE SINGLE-CRYSTALS

To understand the role of thermal stresses in the generation, multipli cation, and propagation of dislocations in CdTe single crystals produc ed by directional solidification, constitutive models which accurately reflect the elastic-viscoplastic behavior of CdTe over a wide range o f temperatures are needed. In this article, the relevant reported mech anical behavior of CdTe is reviewed and discussed. Constitutive equati ons developed for single slip, isothermal behavior of elemental semico nductor crystals by Haasen and co-workers, which include dislocation d ensity as the important internal variable, are then extended to includ e an additional dislocation arrangement internal variable as well as a high-temperature, time-dependent recovery behavior. The constitutive framework is incorporated in a continuum slip framework to include the possibility of multiple slip and to relate slip system shear strain r ates to the macroscopic plastic strain rate. Comparison of the model w ith available experimental data for the small strain case over a wide range of temperatures is presented. Slip system interaction is include d. These constitutive equations can then be used in computational anal yses of thermal stress generation for comparison with characterized cr ystals grown in microgravity and ground-based experiments.