Electromechanical coupling factor of epitaxial gallium nitride doped with magnesium

In a recent paper, Lee et al. (IEEE Trans. Electron Devices 48, 524 (2001)) reported that the piezoelectric constant k(2) of an Mg-doped GaN epilayer was (4.3 +/- 0.3)%, which is much higher than for other III-V materials. In this work, k(2) for a Mg-doped GaN epilayer was independently determined using SAW delay-lines fabricated using aluminum interdigital transducers. The insertion loss of these filters was higher than 80 dB. The upper bound of the electromechanical coupling coefficient (k(2)) of the Mg-doped GaN epilayer was calculated to be 1 x 10(-4)% which is not in agreement with the previously reported value (Lee et al., IEEE Trans. Electron Devices 48, 524 (2001)).