Piezoelectric coefficient of aluminum nitride and gallium nitride

The piezoelectric coefficient d(33) of aluminum nitride (AlN) and gallium nitride (GaN) thin films grown on silicon substrates by molecular beam epitaxy have been measured using a laser interferometer. X-ray diffraction reveals that the AlN and GaN films consist mainly of crystals with a hexagonal wurtzite structure. In order to grow epitaxial GaN films, an AlN film was first deposited on silicon as the buffer layer, so the d(33) measurement for GaN was actually performed on GaN/AlN/Si multilayer systems. The relative permittivity and electrical resistivity of each constituent layer of the film and the potential drop across each layer were determined as a function of frequency. The potential drops were then used to calculate the piezoelectric coefficient d(33) of GaN. After correcting for substrate clamping, d(33) of AlN and GaN were found to be (5.1 +/- 0.1) and (3.1 +/- 0.1) pm V-1, respectively. (C) 2000 American Institute of Physics. [S0021-8979(00)07722-7].