On Apparent Absence of Green Gap in InGaN/GaN Quantum Disks and Wells Grown by Plasma-Assisted Molecular Beam Epitaxy

TL;DR

This study demonstrates that efficient green and red InGaN/GaN quantum wells and disks grown by plasma-assisted molecular beam epitaxy can overcome the green gap issue, due to improved phase uniformity and reduced metallic inclusions.

Contribution

It provides experimental evidence that the green gap can be bypassed in InGaN/GaN structures grown by PAMBE by controlling growth conditions to ensure phase uniformity.

Findings

Green gap absence linked to phase uniformity in growth.

Energetic plasma flux enhances indium incorporation.

Efficient green/red emission achieved with high-quality structures.

Abstract

III-nitride based full-color blue, green and red-light emitting diodes are critically important for a broad range of important applications. To date, however, green or red color III-nitride light emitters grown by conventional growth techniques are limited in efficiency compared to blue emitters. As opposed to metal-organic chemical vapor deposition (MOCVD), while grown by plasma-assisted molecular beam epitaxy (PAMBE), the most intense emission is generally observed in the green spectral region in InGaN/GaN based light emitters. Such counterintuitive phenomenon of efficiency increase with increasing emission wavelength has been observed in both InGaN/GaN quantum-disks in nanowire and planar quantum-wells structures grown by PAMBE. Here, we experimentally show that the apparent absence of green gap in longer green wavelength is due to the difficulty of elimination of indium-rich non-radiative clusters and phase segregation in shorter blue wavelength quantum wells/disks.Excess indium due to the dissociation of the In-N bonds during growth lead to nitrogen vacancies and metallic inclusions. In radio-frequency PAMBE, the energy of the nitrogen radicals was found to be a driving force for indium incorporation.Our detailed growth and associated photoluminescence studies suggests that uniform phase and absence of metallic inclusion is the underlying mechanism of efficient green InGaN/GaN quantum wells/disks grown with sufficiently energetic plasma flux. Our study is valid for achieving very efficient green and red color InGaN/GaN and breaking the green gap bottleneck in quantum wells/disks grown by state-of-the-art high-power plasma-assisted molecular beam epitaxy