Experimental gradient-elastic tensors and chemical bonding in III-V semiconductors

Abstract

Nuclear-acoustic-resonance determinations are made of the magnitudes and relative signs of the two different nonzero components $S_{11}$ and $S_{44}$ of the fourth-rank tensor relating electric field gradients to elastic strains. Measurements are made at 300 K and 10 MHz at the ${\mathrm{Al}}^{27}$ nuclear position in AlSb, at ${\mathrm{Ga}}^{69}$ in GaP, and at ${\mathrm{In}}^{115}$ in InP. Improved measurements are also made at the ${\mathrm{Ga}}^{69}$ nuclear position in GaAs and GaSb, at ${\mathrm{In}}^{115}$ in InAs and InSb, at ${\mathrm{As}}^{75}$ in InAs and GaAs, at ${\mathrm{Sb}}^{121}$ in AlSb, GaSb, and InSb. Theoretical $S_{11}$ and $S_{44}$ are computed assuming them to be sums of ionic and covalent contributions. Ionic contributions are approximated by point charges of the four first neighbors with effective charge $Z^{*}$. Covalent contributions are computed using atomic wave functions and bond polarity values ${\alpha }_p$. $Z^{*}$ and ${\alpha }_p$ are taken from Harrison's bond-optical model (BOM). Comparisons of theoretical and experimental $S_{11}$ give (i) the sign of $Z^{*}$ at the group-V atom as negative, (ii) agreement with the ratio of BOM values of $Z^{*}$ in seven compounds, and (iii) signs and magnitudes of ionic and covalent contributions.