Epitaxy of highly dissimilar transition metal nitride-semiconductor heterostructures with low defect density – the example ScN/GaN(1-100)

The epitaxial combination of structurally and chemically different materials promises to yield heterostructures with enhanced functionalities. For group III-nitrides, the semiconductors commercially applied in light-emitting diodes and high-power electronics, this research field is of particular interest. Heterostructures combining group III-nitrides and transition metal nitrides, for example, exhibit additional functionalities such as superconductivity, ferroelectricity, or photonic resonances, leading to exciting physical phenomena and enabling the fabrication of new, innovative devices. However, due to the mismatch in crystal symmetry between hexagonal wurtzite group III-nitrides and cubic rocksalt transition metal nitrides, rotational twin domains form during the growth of these heterostructures, leading to a high density of twin boundaries. These two-dimensional defects locally reduce the crystal symmetry, resulting in deteriorated properties compared to the bulk.

In this work, we demonstrate twin-free epitaxial growth of rocksalt ScN on wurtzite GaN. In particular, the two-fold symmetric (11̅00) (or M-plane) surface of GaN nanowires and bulk substrates results in ScN layers with an unexpected orientation-relationship, for which the large mismatch along the [001] direction of ScN is accommodated by a coincidence site lattice. In contrast to growth on the conventional GaN(0001) (or C-plane) surface where twinning is inevitable, the two-fold symmetry of the growing ScN(110) film matches that of the underlying GaN(11̅00) substrate, thus providing a commensurate ScN/GaN interface. This low-symmetry interface is the key to avoid twin formation.

Our approach opens a new route to combine the wurtzite III-nitrides AlN, GaN and InN with rocksalt transition metal nitrides like ScN, ZrN, HfN, TiN, CrN and NbN with unprecedented structural quality. This successful integration of transition metal nitrides on group III-nitrides with low defect densities opens up new prospects for improving the performance of existing devices or creating innovative new ones.

Authors: Philipp John, Achim Trampert, Duc Van Dinh, Domenik Spallek, Jonas Lähnemann, Vladimir Kaganer, Lutz Geelhaar, Oliver Brandt, and Thomas Auzelle
Title: ScN/GaN(11̅00): A New Platform for the Epitaxy of Twin-Free Metal–Semiconductor Heterostructures
Source: Nano Letters 24, 6233 (2024)
DOI: 10.1021/acs.nanolett.4c00659