Allotropic Ga$_2$Se$_3$/GaSe nanostructures grown by van der Waals epitaxy: Narrow exciton lines and single-photon emission

TL;DR

This paper demonstrates the growth of Ga$_2$Se$_3$/GaSe nanostructures via van der Waals epitaxy, showing they emit narrow exciton lines with polarization and single-photon emission, useful for quantum technology applications.

Contribution

It introduces a method to control phase formation in epitaxial GaSe-based nanostructures, enabling narrow exciton lines and single-photon emission for quantum devices.

Findings

Nanostructures exhibit narrow exciton lines due to quantum confinement.

They show linear polarization from Ga vacancy ordering.

Single-photon emission with $g^{(2)}(0)\sim$0.1 at 10 K.

Abstract

The ability to emit narrow exciton lines, preferably with a clearly defined polarization, is one of the key conditions for the use of nanostructures based on III-VI monochalcogenides and other layered crystals in quantum technology to create non-classical light. Currently, the main method of their formation is exfoliation followed by strain and defect engineering. A factor limiting the use of epitaxy is the presence of different phases in the grown films. In this work, we show that control over their formation makes it possible to create structures with the desired properties. We propose Ga$_2$Se$_3$/GaSe nanostructures by van der Waals epitaxy with a high VI/III flux ratio as a source of narrow exciton lines. Actually, these nanostructures are a combination of allotropes: GaSe and Ga$_2$Se$_3$, consisting of the same atoms in different arrangements. The energy position of the narrow lines is determined by the quantum confinement in Ga$_2$Se$_3$ inclusions of different sizes in the GaSe matrix, similar to quantum dots, and their linear polarization is due to the ordering of Ga vacancies in a certain crystalline direction in Ga$_2$Se$_3$. Such nanostructures exhibit single-photon emission with second-order correlation function $g^{(2)}(0)\sim$0.1 at 10 K that makes them promising for quantum technologies.