Shear piezoelectric coefficients of gallium nitride and aluminum nitride

We have developed a direct method of measuring the shear strain using a las er-based interferometer. The method was applied to the measurement of the d (15) coefficient for wurtzite GaN and AlN. A value for d(15) 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 d(15) for GaN has also been measured to be 3.1 +/- 0.2 pm V-1. (C) 1999 American Institute of Physics. [S0003-6951(99)025 51-6].