Shear piezoelectric coefficients of gallium nitride and aluminum nitride

Abstract
We have developed a direct method of measuring the shear strain using a laser-based interferometer. The method was applied to the measurement of the d15 coefficient for wurtzite GaN and AlN. A value for d15 of 3.6±0.2 pm V−1 for AlN has been obtained, in good agreement with values quoted in the literature. The value of d15 for GaN has also been measured to be 3.1±0.2 pm V−1.