Determination of HgCdTe elasto-plastic properties using nanoindentation

Abstract

Depth sensing indentation has been used to investigate the elasto-plastic behavior of Hg 0.7 Cd 0.3 Te prepared by molecular beam epitaxy, liquid phase epitaxy, as well as of bulk Hg 0.7 Cd 0.3 Te prepared by the modified Bridgman method. It was found that Hg 0.7 Cd 0.3 Te was characterized by a modulus of elasticity of E avg ; 50 GPa and hardness of H avg ; 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 ;10% elastic and ;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 1.1ÿ1.8 GPa. This onset and subsequent flow of plasticity is postulated to be associated with the spontaneous nucleation and propagation of dislocations.

Mechanical and Thermal Properties

“…Available experimental data of Young's modulus for MCT, which are included in Table 8.3, originate from microindentation measurements of Kurilo et al [75] for bulk crystals (x = 0, 0.2, 1.0) and nanoindentation measurements Martyniuk et al [79,80] for MBE, LPE, as well as bulk material (x = 0.3), which are in good agreement with each other. Since the indentation tip while deforming the crystal structure induces strains locally, it produces nearly uniform strains around dislocations and the experimental Young's modulus values are in closer agreement with the Young's modulus values from Voigt rather than Reuss averaging.…”

“…The lines that join the data points of Barbot et al [104] in (a) and the lines in the inset of (b) are simply a guide for the eye. [80], were observed to increase with decreasing depth of indentation for indentation contact depth less than ∼300 nm, independent of growth method. This characteristic dependence of hardness on the indentation depth has often been referred to as the indentation size effect, and is expected to be especially pronounced in soft crystalline materials.…”

“…Numerous data are available on Hg 1−x Cd x Te hardness at room temperature as a function of composition, x , for various growth methods: quenched ingots [85,86], travelling heater method (THM) [86][87][88], Bridgman method [80,86,[89][90][91], isothermal vapor phase epitaxy (ISOVPE) [92,93], LPE [80,92], MBE [79] or other [94,95]. Myles and Ekpenuma [98], Eqn.…”

“…8. 25 Sharma et al [85], Hv, quenched Schenk and Fissel [86], Hv, quenched Schenk and Fissel [86], Hv, THM Schenk and Fissel [86], Hv, Bridgeman Triboulet et al [87], Hv, THM Barbot et al [88], Hv, THM Fissel and Schenk [96], Hv, THM Cole et al [89], Hv, Bridgeman Andrews et al [90], which may be related to the dependence of hardness on loading velocity and/or loading time [75,96], or significant amounts of creep [80]. In addition, Martyniuk et al [80] have shown that the measured MCT hardness increases with decreasing indentation depth, an effect that is expected to be especially pronounced for soft crystalline materials [97], and that could also contribute to the degree of scatter.…”

“…The reviewed deformation characteristics mostly encompass compression [104], bending [105,106], and nanoindentation [79,80] testing of the MCT material.…”