THEORY AND APPLICATION OF MICROINDENTATION IN STUDIES OF GLIDE AND CRACKING IN SINGLE-CRYSTALS OF ELEMENTAL AND COMPOUND SEMICONDUCTORS

The microhardness of Si (MP 1688 K), GaP (1623 K), GaAs (1510 K) and InP (1327 K) single crystals was determined by indentation (Vicker's hardness, VHN) of low-index facets at loads of 5-100 g at 296-673 K, complementing earlier work on Ge and InSb. In the brittle range, extending up to about 0.35 T(melt) (K), cracking occurred preferentially along the diagonals of the identations, and was observed at all loads, with the possible exception of the lowest (5 g) in the case of InP at 289 K. At higher temperatures the relative orientations of crack and slip traces on the crystal surface, as observed by SEM, suggested that cracks nucleated preferentially at the slip-band intersection, as was also noted by Hirsch et al. (Phil. Mag. 3 (1985) 759) in GaAs above 600 K. As earlier in Ge, the VHN was found to depend on the load, L, as L(p), and on the identation diameter, d, as d(n), with p = 1/2 and n = 2, as required by the model of identation plasticity of Banerjee and Feltham [4, 5], but higher p and n values were found if chipping at the identation edges was evident. The effect was related to the resulting decrease in identation diameter due to the work lost, through chipping, by the indenter. Above about 0.35 T(melt) (K), relaxation of the dislocation structures entails a decrease of p and n; both parameters tend to zero as T --> T(melt). Shear and tensile stresses seem to co-operate in the process of plastic deformation, the role of normal stresses, acting across slip planes, predominating in the 'brittle' range.