N-polar ScAlN and HEMTs grown by molecular beam epitaxy

Molecular beam epitaxy of single-phase wurtzite N-polar ScxAl1-xN (x similar to 0.11-0.38) has been demonstrated on sapphire substrates by locking its lattice-polarity to the underlying N-polar GaN buffer. Coherent growth of lattice-matched Sc0.18Al0.82N on GaN has been confirmed by x-ray diffraction reciprocal space mapping of the asymmetric (105) plane, whereas lattice-mismatched, fully relaxed Sc0.11Al0.89N and Sc0.30Al0.70N epilayers exhibit a crack-free surface. The on-axis N-polar crystallographic orientation is unambiguously confirmed by wet chemical etching. High electron mobility transistors using N-polar Sc0.18Al0.82N as a barrier have been grown on sapphire substrates, which present the existence of well confined two-dimensional electron gas. A Hall mobility of similar to 564 cm(2)/Vs is measured for a 15-nm-thick Sc0.18Al0.82N barrier sample with a sheet electron concentration of 4.1x10(13) cm(-2), and the corresponding sheet resistance is as low as 271 Omega/sq. The polarity-controlled epitaxy of ScxAl1-xN provides promising opportunities for applications in high-frequency and high-power electronic and ferroelectric devices. Published under an exclusive license by AIP Publishing.

Automated summary

Molecular beam epitaxy of single-phase wurtzite N-polar ScxAl1-xN has been demonstrated on sapphire substrates, with high electron mobility transistors showing well confined two-dimensional electron gas with high mobility and low sheet resistance. The controlled epitaxy of ScxAl1-xN presents promising opportunities for applications in high-frequency and high-power electronic and ferroelectric devices.