Epitaxial ScAlN grown by molecular beam epitaxy on GaN and SiC substrates

ScxAl1-xN is a promising ultra-wide bandgap material with a variety of potential applications in electronic, optoelectronic, and acoustoelectric devices related to its large piezoelectric and spontaneous polarization coefficients. We demonstrate growth of ScxAl1-xN on GaN and SiC substrates using plasma-assisted molecular beam epitaxy with x = 0.14-0.24. For metal-rich growth conditions, mixed cubic and wurtzite phases formed, while excellent film quality was demonstrated under N-rich growth conditions at temperatures between 520 and 730 degrees C. An rms roughness as low as 0.7 nm and 0002 rocking curve full-width at half maximum as low as 265 arc sec were measured for a Sc0.16Al0.84N film on GaN. To further demonstrate the quality of the ScAlN material, a high-electron-mobility transistor heterostructure with a Sc0.14Al0.86N barrier, GaN/AlN interlayers, and a GaN buffer was grown on SiC, which showed the presence of a two-dimensional electron gas with a sheet charge density of 3.4 x 10(13) cm(-2) and a Hall mobility of 910 cm(2)/V.s, resulting in a low sheet resistance of 213 Omega/square.