Piezoelectric coefficient of aluminum nitride and gallium nitride

Abstract

The piezoelectric coefficient d₃₃ 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 d₃₃ 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 d₃₃ of GaN. After correcting for substrate clamping, d₃₃ of AlN and GaN were found to be (5.1±0.1) and (3.1±0.1) pm Vˉ¹, respectively.