Heteroepitaxial growth of GaN/Si (111) junctions in ammonia-free atmosphere: Charge transport, optoelectronic, and photovoltaic properties

Abstract

We report the catalyst-free growth of gallium nitride (GaN) nanostructures on n-Si (111) substrates using physical vapor deposition via thermal evaporation of GaN powder at 1150 °C in the absence of NH3 gas. Scanning electron microscopy and energy dispersive x-ray analysis indicate that the growth rate of GaN nanostructures varies with deposition time. Photoluminescence spectra showed the suppression of the UV emission and the enhancement of the visible band emission with increasing the deposition time. The fabricated GaN nanostructures exhibited p-type behavior at the GaN/Si interface, which can be related to the diffusion of Ga into the Si substrate. The obtained lowest reflection and highest transmittance over a wide wavelength range (450–750 nm) indicate the high quality of the fabricated GaN films. Hall-effect measurements showed that all fabricated films have p-type behavior with decreasing electron concentration from 1021 to 1012 cm−3 and increasing the electron mobility from 50 to 225 cm2/V s with increasing the growth time. The fabricated solar cell based on the 1 h-deposited GaN nanostructures on n-Si (111) substrate showed a well-defined rectifying behavior with a rectification ratio larger than 8.32 × 103 in dark. Upon illumination (30 mW/cm2), the 1 h-deposited heterojunction solar cell device showed a conversion efficiency of 5.78%. The growth of GaN in the absence of NH3 gas has strong effect on the morphological, optical, and electrical properties and consequently on the efficiency of the solar cell devices made of such layers.