Determination of HgCdTe Elasto-Plastic Properties using Nanoindentation

Depth sensing indentation has been used to investigate the elasto-plastic behavior of Hg0.7Cd0.3Te prepared by molecular beam epitaxy, liquid phase epitaxy, as well as of bulk Hg0.7Cd0.3Te prepared by the modified Bridgman method. It was found that Hg0.7Cd0.3Te was characterized by a modulus of elasticity of E-avg similar to 50 GPa and hardness of H-avg similar to 0.66 GPa, independent of growth technology. The measured hardness was observed to increase with decreasing size of indentation owing to the nucleation of dislocations within the plastic zone. The elasto-plastic response of the samples to nanoindentation was observed to be purely elastic at low indentation depths and developed into similar to 10% elastic and similar to 90% plastic response, with an increase in penetration contact depth to above 100 nm exhibiting significant amounts of creep. The transition from purely elastic to elasto-plastic behavior has been observed to be marked by discontinuities, or "pop-in" events in the indenter load-penetration curves, with the indentation zone maximum sheer stress varying with HgCdTe growth method in the range 1.1-1.8 GPa. This onset and subsequent flow of plasticity is postulated to be associated with the spontaneous nucleation and propagation of dislocations.