Polarity Control of LP-MOVPE GaN using N₂ the Carrier Gas

Abstract

The polarity control of GaN films grown on c-plane sapphire substrates by LP-MOVPE using N₂ as carrier and diluent gas was investigated in detail. The polarity type depended on the substrate preparation prior to the high temperature (HT) GaN growth. Device-quality Ga-polar GaN was obtained by using a low temperature (LT) AlN buffer layer followed by a specific annealing process. Optimized buffer layer thickness was 10 nm, with an annealing time of 20 min and a temperature of 1050 °C. By using these conditions for the buffer layer growth, mirror-like Ga-polarity GaN was grown using a V/III ratio of 100. The full width at half maximum (FWHM) of Ga-polar GaN films was 360 arcsec for the symmetric (00.2) reflection and 640 arcsec for the skew-symmetric (30.2) reflection. The surface roughness was measured by AFM to be 0.2 nm RMS and the growth rate was estimated at 2.0 μm/hr. These results indicated that by exclusively using N₂ carrier gas, one can achieve films of the same quality as those more commonly grown by using H₂ carrier gas.