Correlation between electrical and surface properties of n-GaN on sapphire grown by metal-organic chemical vapor deposition

Lightly doped n-GaN epilayers were grown by metal-organic chemical vapor deposition (MOCVD) on sapphire substrates. The grown n-GaN epilayers were characterized using atomic force microscopy (AFM), X-ray diffraction (XRD), photoluminescence and Hall effect measurements. Enhanced PL intensity and low dark spot density (DSD) were observed on the aligned step structure n-GaN. The samples with these aligned step structure showed high electron mobilities with good structural and optical properties, while the samples with the anisotropic step structure showed broadened XRD FWHM values, low mobilities, and poor structural and optical properties. The low Hall mobility of n-GaN is due to the scattering of charged threading dislocations. A clear correlation was observed between Hall mobility and DSD by AFM. The AFM surface observation is also a better method for the evaluation of the electron mobility of lightly doped MOCVD grown n-GaN.