Donor nonuniformity in undoped and Si doped $n-GaN$ prepared by epitaxial lateral overgrowth

Local donor concentrations were measured in the regions of lateral overgrowth and in the normal vertical growth regions of $n-GaN$ films prepared by epitaxial lateral overgrowth (ELOG). The films were doped with Si to various concentrations. The local donor densities were determined from measurements of the collection efficiency dependence of the electron beam induced current (EBIC) on the energy of the probing electron beam. This dependence was compared with the results of theoretical modeling using the local donor density and diffusion length of charge carriers as fitting parameters. The results show that the donor concentration in the ELOG regions is systematically more than two times lower than the concentration in the vertical growth regions in the gaps of the $SiO2$ mask used for selective growth. The observed difference is ascribed to the anisotropy of the Si incorporation efficiency. Comparison of these EBIC results with the results of capacitance-voltage profiling obtained on large area Schottky diodes shows that the latter yield the donor concentration close to the concentration in the laterally overgrown regions.