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

Nuclear-acoustic-resonance determinations are made of the magnitudes and relative signs of the two different nonzero components S₁₁ and S₄₄ of the fourth-rank tensor relating electric field gradients to elastic strains. Measurements are made at 300 K and 10 MHz at the Al²⁷ nuclear position in AlSb, at Ga⁶⁹ in GaP, and at In¹¹⁵ in InP. Improved measurements are also made at the Ga⁶⁹ nuclear position in GaAs and GaSb, at In¹¹⁵ in InAs and InSb, at As⁷⁵ in InAs and GaAs, at Sb¹²¹ in AlSb, GaSb, and InSb. Theoretical S₁₁ and S₄₄ 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 αₚ. Z* and αₚ are taken from Harrison's bond-optical model (BOM). Comparisons of theoretical and experimental S₁₁ 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.