preprints.org > chemistry and materials science > electronic, optical and magnetic materials > doi: 10.20944/preprints202405.0200.v1

Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

Version 1 : Received: 3 May 2024 / Approved: 4 May 2024 / Online: 6 May 2024 (08:47:18 CEST)

In the present work, diamond films have been grown on GaN-on-Sapphire substrates by chemical vapor deposition (CVD) with the addition of nitrogen to the standard H2/CH4 precursor recipe. 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% N2 gas was gradually added to the H2 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 sp3 bonded diamond film produced by nitrogen addition was found to be co-deposited along with a considerable amount of other non-diamond carbon phases (D - disordered graphite, G - crystalline graphite, TPA - trans-polyacetylene) and qualitatively all the diamond films were 50% pure (Raman peak ratio Isp3 / ID). The FWHM of the sp3 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 N2. 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 N2 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. Nitrogen addition was thus found to be detrimental for growing CVD diamond films over GaN surfaces. The electrical resistivity of the uncoated GaN was initially measured to be 22.2 Ω-cm. However, the resistivity rose to 1.59×106 Ω-cm after the nitrogen assisted film deposition; due to the GaN etching - thereby exposing the underlying insulating sapphire substrate.

CVD; etching; diamond; GaN; microstructure; properties

Chemistry and Materials Science, Electronic, Optical and Magnetic Materials

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