Electrical characterisation of hole traps in n-type GaN

We have used thermally stimulated capacitance (TSCAP) and optical deep level transient spectroscopy (O-DLTS) to detect and characterise hole traps in n-type GaN grown by epitaxial lateral overgrowth (ELOG) organo-metallic vapour phase epitaxy (OMVPE). Semi-transparent Ni Schottky barrier diodes (SBDs) were used to probe the space charge region of the GaN layer. Optical excitation was achieved using an ultraviolet light emitting diode with sub-bandgap energy photons at a wavelength of 380 nm. Two hole traps with activation enthalpies of 0.25 eV and 0.85 eV with respect to the valence band were found to be present in concentrations of 5 x 10(14) and 2 x 10(15) cm(-3). This is almost two orders of magnitude higher than the concentration of the electron traps present in this material. We have also found that 1.8 MeV proton implantation introduced additional shallow level hole traps with activation enthalpies of 0.19 eV and 0.23 eV, respectively.