Enhanced etching of GaN with N2 gas addition during CVD diamond growth

Abstract

Diamond on GaN materials processing is not straight-forward, as GaN is susceptible to a quasi-pure hydrogen CVD plasma etching. 1%, 3% and 5% N-2 gas was gradually added to the H-2 gas with fixed 6% CH4 in the recipe to promote the growth of diamond nanocrystals. Different types of microstructures were produced, with addition of nitrogen to the precursor gas recipe. Nitrogen gas changes the diamond film microstructure from faceted to spherical grains, with signs of GaN etching. The FWHM of the sp(3) carbon Raman peak was calculated to be 6.5 cm(-1), when there was no nitrogen gas in the precursor recipe, which deteriorates to a large extent after successive addition of N-2. Fourier transform infrared spectroscopy (FTIR) showed a strong presence of the nitrogen related defects (peak positions at 1190 and 1299 cm(-1)) inside the nanocrystalline diamond (NCD) films grown with N-2 addition. GaN layer etching from the base substrate by the CVD plasma was clearly evidenced by energy dispersive X-ray spectra (EDS) of the deposited films. Al elemental EDS peaks from the base sapphire substrate were observed for the films grown with nitrogen addition, but no Ga EDS peaks were detected. X-ray diffraction (XRD) micrographs further supported the enhanced GaN etching phenomenon. The electrical resistivity of the uncoated GaN was initially measured to be 22.2 Omega-cm. However, the resistivity rose to 1.59 x 10(6) Omega-cm after the nitrogen assisted film deposition; due to the GaN etching - thereby exposing the underlying insulating sapphire substrate.