Piezoelectric coefficient of GaN measured by laser interferometry

A Mach-Zehnder type heterodyne interferometer was used to measure the d(33) coefficient of wurtzite gallium nitride (GaN) films. The 140 nm thick GaN film, with a 30 nm thick aluminum nitride (AlN) buffer layer, had been grown by molecular beam epitaxy (MBE) on (1 0 0) or (1 1 1) silicon substrates. The measurement of the piezoelectric coefficient was made with a spatial resolution (laser beam diameter) of 100 mu m. Voltage drop across the aluminum nitride buffer layer was estimated and used in calculating the piezoelectric coefficient of GaN. For rigidly mounted samples, the measured d(33) was 2.13 pm/V. (C) 1999 Elsevier Science B.V. All rights reserved.