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

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