Molecular Beam Epitaxy of 2D-layered Gallium Selenide on GaN substrates

TL;DR

This paper demonstrates the growth of high-quality, large-area gallium selenide (GaSe) 2D layers on GaN substrates using molecular beam epitaxy, revealing phase control and epitaxial relationships crucial for device applications.

Contribution

It introduces a two-step molecular beam epitaxy method for growing high-quality, epitaxial GaSe layers with phase control on GaN substrates, advancing 2D material synthesis.

Findings

High-quality GaSe films achieved on GaN with complete surface coverage.

Two-step growth method enables phase control and epitaxial alignment.

Observation of both { extbeta}- and { extepsilon}-GaSe phases during growth.

Abstract

Large area epitaxy of two-dimensional (2D) layered materials with high material quality is a crucial step in realizing novel device applications based on 2D materials. In this work, we report high-quality, crystalline, large-area gallium selenide (GaSe) films grown on bulk substrates such as c-plane sapphire and gallium nitride (GaN) using a valved cracker source for Se. (002)-oriented GaSe with random in-plane orientation of domains was grown on sapphire and GaN substrates at a substrate temperature of 350-450 C with complete surface coverage and smooth surface morphology. Higher growth temperature (575 C) resulted in the formation of single-crystalline {\epsilon}-GaSe triangular domains with six-fold symmetry confirmed by in-situ reflection high electron energy diffraction (RHEED) and off-axis x-ray diffraction (XRD). A two-step growth method involving high temperature nucleation of single crystalline domains and low temperature growth to enhance coalescence was adopted to obtain continuous (002)-oriented GaSe with an epitaxial relationship with the substrate. While six-fold symmetry was maintained in the two step growth, {\beta}-GaSe phase was observed in addition to the dominant {\epsilon}-GaSe in cross-sectional scanning transmission electron microscopy images. This work demonstrates the potential of growing high quality 2D-layered materials using molecular beam epitaxy and can be extended to the growth of other transition metal chalcogenides.