Electron density gradients in ammonothermally grown Si-doped GaN

Charge homogeneity in heavily Si-doped ammonothermal GaN has been studied by confocal micro-Raman measurements. The polarized Raman spectra indicate a high crystalline quality of the sample. On the N-polarity growth sector we observe both branches (L+, L-) of the phonon-plasmon coupled modes. The free-electron density, which is derived from a line-shape fit to the L+ mode, displays an in-depth gradient with a decreasing density when the top surface is approached. The Raman spectra of the Ga-polarity growth sector do not show any trace of phonon-plasmon coupled modes, suggesting a lower Si incorporation and/or the presence of compensating deep levels. (C) 2014 The Japan Society of Applied Physics