Raman microscopy of lateral epitaxial overgrowth of GaN on sapphire

We have used confocal Raman microscopy to investigate lateral epitaxially o vergrown (LEO) GaN on sapphire substrates. The one-phonon Raman spectra are consistent with pyramidal growth of the GaN before coalescence has occurre d. The position and asymmetric line shape of the Al-1 longitudinal optical (LO) phonon demonstrate that the LEO GaN is doped. The dopant is most likel y Si from the SiN mask used to produce the LEO GaN. The carrier concentrati on is estimated to be 1 x 10(17) cm(-3). We have also measured the optical branch of the second-order Raman scattering from the LEO GaN.