Mechanical properties of undoped GaAs. Part I: Yield stress measurements

The present series of papers reports on the yield and fracture properties of undoped single crystal GaAs. In part I, the results of uniaxial compression tests over a range of temperatures, 200-550 oC, and strain rates, 2.5 x 10-5-2 x 10-4 s-1 are presented. Previous reports on deformation of GaAs have mostly involved tests in the ductile regime (T ≥ 400 oC). Although there are a few reports on low-temperature deformation tests in the brittle regime of GaAs, they were all performed in the presence of a hydrostatic pressure. The present experiments extend the deformations from the ductile to the brittle regime of the material without the superposition of a hydrostatic stress. In this way, the temperature- and strain rate dependence of the yield stress τy of GaAs has been determined. The results show an abrupt change in the deformation mechanism at a critical temperature Tc2 that systematically increases with the strain rate ε.. The critical temperature Tc2 is in the same range as the brittle-to-ductile transition (BDT) temperature TBDT of GaAs and follows the same trend with respect to changes in the strain rate. In part II of this series, we report on direct measurement of TBDT of GaAs at different strain rates to see how it compares with the critical temperatures Tc2, obtained from uniaxial compression tests. For the measurements of TBDT, we have used the technique of four-point bend testing. Finally, in part III, the same undoped GaAs material is deformed by static and dynamic (displacement-sensitive) indentation tests over a wide range of temperatures and the results compared with those obtained from compression experiments and four-point bend tests. The results show that the indentation BDT temperature TIBDT is significantly lower than the value of TBDT obtained from direct fracture experiments (part II), presumably because of the superimposed hydrostatic component present in an indentation. The microstructure of samples deformed by compression and indentation tests are also investigated by transmission electron microscopy and dislocation mechanisms are discussed to interpret the plastic and fracture properties of GaAs