Influence of GaN polarity and intermediate-temperature buffer layers on strain relaxation and defects

The dependence of strain relaxation and consequent generation defects on Gallium nitride (GaN) polarity and intermediate-temperature buffer layer (ITBL) has been observed by Raman scattering, photoluminescence (PL) and monoenergetic positron beam techniques. Raman scattering studies have indicated that tensile stress prefers and compress stress is present in N-polar and Ga-polar films, respectively. Furthermore, ITBL relaxes strains in Ga-polar GaN films more effectively than in N-polar GaN films. PL results show that peak shifts due to the effect of polarity and ITBL. Depth resolved defect-sensitive S parameter measurements, using monoenergetic positron beam, exhibit larger S parameter and shorter positron effective diffusion length in N-polar GaN samples than those in Ga-polar films. When ITBL is added, S   parameter decreases and effective diffusion length increases in both groups. Hall mobility and carrier concentration measurement manifest a reduction of dislocation line and electrons trap centers such as VGaVGa or Ga vacancy clusters.