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Keywords:

  • gallium nitride;
  • Gunn-diode;
  • micro-Raman spectroscopy;
  • carrier profile;
  • Kelvin probe force microscopy

Abstract

Scanning confocal micro-Raman and PL spectroscopy, Kelvin probe force microscopy (KPFM) and electrostatic force gradient microscopy (EFGM) were applied to study the concentration profiles of free carriers by scanning the cleaved edge along the growth direction of vertical n+/n0/n+-GaN Gunn-diode structure. The vertical frequency profile of the L branch of the plasmon-LO-phonon modes was used to evaluate the concentration of free charge carriers. Obtained significant contrast through the undoped n0-GaN region validates the expected reduction in carrier concentration. Variation of the local contrast in cross-section KPFM and EFGM electrical images reflects the topology of the device structure and makes it possible to estimate electronic properties of individual GaN layers as well as interface boundaries. The carrier profiles determined from the Raman data and KPFM measurements are in good agreement. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)