Fractional-Monolayer 2D-GaN/AlN Structures: Growth Kinetics and UVC-emitter Applications

TL;DR

This study investigates the growth, properties, and UVC-emission applications of fractional-monolayer GaN/AlN quantum wells, revealing how growth mechanisms influence luminescence and demonstrating their potential as powerful UVC emitters.

Contribution

It introduces a phenomenological model for fractional-ML QWs based on growth mechanisms and validates it with experimental luminescence data, advancing understanding of ultra-thin GaN/AlN heterostructures.

Findings

Fractional-ML QWs exhibit growth mechanism-dependent luminescence properties.

The proposed model describes fractional-ML QWs as arrays of quantum disks or ribbons.

GaN/AlN heterostructures show high-power UVC emission with linear power dependence.

Abstract

The paper reports on fundamental properties of the GaN/AlN quantum wells (QWs) with nominal subcritical thicknesses of 0.75-2 monolayers (MLs). They are grown by plasma-activated molecular beam epitaxy, varying either the nominal thickness or the gallium-to-nitrogen flux ratio. In situ monitoring reveals difference in 2D nucleation and step-flow growth modes of the QWs. The emission charactestics of QWs with integer thicknesses of 1 and 2 MLs depend weakly on the growth mechanism. In contrast, the intensity and spectral position luminescence of QWs with fractional-ML thicknesses are determined by the growth mechanism. Using ab initio calculations, a phenomenological model is proposed that describes fractional-ML QWs either as arrays of 2D quantum disks or as arrays of 2D quantum ribbons, in cases where 2D nucleation or step-flow growth mechanisms predominate, respectively. This model is generally consistent with experimental data on photo- and cathodoluminescence of heterostructures with multiple (250) GaN/AlN QWs. These heterostructures, when pumped by electrom beam at an energy 12.5 keV with a maximum pulse current of 2 A, exhibit linear current dependences of optical peak powers up to 1 and 37 W for wavelengths of 228 and 256 nm, respectively, making them promising for use as powerfull ultraviolet-C emitters.