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

TL;DR

This study reports the growth and detailed characterization of (113)-oriented ScN layers on AlN templates, revealing unique surface orientations, in-plane relationships, optical properties, and impurity conduction mechanisms relevant for device applications.

Contribution

First demonstration of (113) surface orientation in ScN layers grown by plasma-assisted molecular beam epitaxy with detailed structural and electronic characterization.

Findings

Confirmed pure (113) surface orientation with rotational twins.

Identified two in-plane relationships between ScN(113) and AlN.

Observed broad photoluminescence peak at 2.16 eV and impurity band conduction.

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 $(60 \pm 3)\,\mathrm{meV}$.