Alumina-rich spinel: A new substrate for the growth of high quality GaN-based light-emitting diodes

A new substrate material, alumina-rich spinel, with better thermal and lattice match to GaN than sapphire, has been developed for growing high-quality GaN-based light-emitting diodes (LEDs). As 1:3 spinel (1 MgO for 3 Al2O3), MgAl6O10, is chemically close to sapphire, Al2O3, we successfully replicated on (1 1 1)-oriented spinel wafers the GaN metal-organic chemical vapor deposition conditions developed for c-plane sapphire. This enabled the simultaneous growth of GaN on both substrates. The resulting GaN layers are structurally, optically and electrically as good on 1:3 spinel as on sapphire. We therefore grew, still simultaneously on both substrates, InGaN LEDs with peak emission wavelengths ranging from 450 nm (blue) to 550 nm (yellow-green). Their electroluminescence (EL) was found to be brighter on 1:3 spinel than on sapphire, with the light output increasing almost linearly prior to breakdown in both cases. The EL full-width at half-maximum was also systematically narrower on 1:3 spinel than on sapphire, again confirming the high quality of the LEDs grown on this new substrate material.