Confocal Raman depth-profile analysis of the electrical and structural properties in III-nitride structures

Scanning confocal Raman spectroscopy was used to non-destructively evaluate the structural and electronic properties of n+/n0/n+-GaN Gunn-diode structures. The depth profiles of the free carrier concentration and mobility were obtained from a line shape analysis of the ω–, ω+ coupled phonon-plasmon modes. It was found that the intensity profiles of the Raman polar A1(LO) phonon mode depend on the thickness of the undoped n0 layer, while the intensity profiles of the nonpolar E2high mode were unaffected by the doping. The change in frequency and linewidth of E2high mode throughout the thickness of the GaN layers, however reveal structural inhomogeneity in the diode structures. The carrier concentration and mobility exhibit only slight variations with thickness with the largest variation being at the free surface of the device. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)