Rock-salt ScN(113) layers grown on AlN$(11\bar{2}2)$ by plasma-assisted molecular beam epitaxy

Abstract

Transition-metal nitrides constitute a versatile class of materials with diverse properties and wide-ranging applications. Exploring new surface orientations and uncovering novel properties can enable innovative material configurations with tailored functionalities for device integration. Here, we report the growth and characterization of (85-210)-nm-thick undoped ScN layers on AlN$(11\bar{2}2)$/Al${}_2$O${}_3$$(10\bar{1}0)$ templates via plasma-assisted molecular beam epitaxy. X-ray diffractometry and transmission electron microscopy confirm a pure (113) surface orientation with rotational twins. Two distinct in-plane relationships between ScN(113) and AlN$(11\bar{2}2)$ have been identified: the dominant $[1\bar{1}0{]}_{\mathrm{ScN}}\parallel [\bar{1}\bar{1}23{]}_{\mathrm{AlN}}$ and $[33\bar{2}{]}_{\mathrm{ScN}}\parallel [1\bar{1}00{]}_{\mathrm{AlN}}$ (under tensile-compression), and the less prevalent $[\bar{1}\bar{2}1{]}_{\mathrm{ScN}}\parallel [1\bar{1}00{]}_{\mathrm{AlN}}$ and $[7\bar{4}\bar{1}{]}_{\mathrm{ScN}}\parallel [\bar{1}\bar{1}23{]}_{\mathrm{AlN}}$ (under biaxial compression). Broad photoluminescence spectra with a peak emission energy of $\approx 2.16\mathrm{eV}$ originate from the lowest direct gap at the $\mathbf{X}$ point of the ScN band structure. Temperature-dependent Hall-effect measurements (4-380 K) reveal that impurity band conduction dominates. The electron mobility is primarily limited by optical phonon scattering, characterized by an effective phonon energy of $(60\pm 3)\mathrm{meV}$.