Thermal Annealing of Cubic‐InGaN/GaN Double Heterostructures

Abstract

We have performed annealing experiments with c-InGaN/GaN double heterostructures in order to obtain information on the thermal stability and the formation process of In-rich clusters in the InGaN layers. While the as grown samples showed a dominating luminescence at about 2.3 eV, the annealed samples showed a new luminescence peak at 2.8-3.0 eV which may be due to a band gap emission of a regenerated layer with an In-content of about x ¼ 0.20. These results are corroborated by micro Raman spectroscopy. Our annealing experiments show that at elevated temperatures In-atoms can diffuse in c-InGaN layers while In-rich aggregates are stable at growth temperature.Introduction Recent X-ray diffraction and micro-Raman measurements gave first evidence of In-rich inclusions in c-InGaN layers [1]. Resonant Raman measurements show that the PL of these layers is related to In-rich nanometer-size quantum-dot (QD) like structures [2]. Investigations of the structure and photoluminescence (PL) from c-InGaN/GaN double heterostructures (DHs) showed the importance of the QD-like In-rich structures for the radiative recombination of electron hole pairs [3]. Evidence for radiative recombination of excitons localized in nanostructures such as In-rich clusters in cubic InGaN multiple quantum wells (MQWs) has also been reported in Ref. [4].In this paper we report on annealing experiments which were performed in order to obtain further insight into the formation process and the thermal stability of the In-rich clusters in our c-InGaN/GaN DHs.

Molecular beam epitaxy of cubic III‐nitrides on GaAs substrates

“…These results together with Raman scattering experiments [121] suggest that the In-rich phase in cInGaN layers is thermodynamically stable up to temperatures of about 700 °C. However, at about 750 °C diffusion of In out of the In-rich clusters into the InGaN-layers seems to be effective.…”

“…Annealing experiments were performed to gain insight into the formation process of the In-rich phase in c-In x Ga 1-x N/GaN DHs [121]. Samples were annealed in vacuum for 10 hours.…”

Progress in Indium Gallium Nitride Materials for Solar Photovoltaic Energy Conversion

“…These clusters present a problem to In x Ga 1Àx N photovoltaic performance as they have been shown to act as efficient recombination centers for excitons. [107] A number of photoluminescence (PL) studies of In x Ga 1Àx N films have found emission peaks at a constant energy (2.3 to 2.5 eV) insensitive to varying indium contents. [108,109] This strong emission peak provides evidence for the existence of an In-rich phase which, while only representing a small fraction of the film's volume, dominates the emission mechanism of the film.…”

“…Various authors have reported the presence of In-rich quantum wells and quantum dots in these clusters. [80,107] One author attributes the PL emission peaks to 15-nm-diameter quantum dot structures with an indium content of x = 0.56. [108] It is clear the intense PL emissions reported are a direct product of radiative recombination in these In-rich clusters, which would be expected due to their lower band gap relative to the surrounding bulk matrix.…”

Overcoming the Miscibility Gap of GaN/InN in MBE Growth of Cubic InxGa1–xN

“…However, growing metastable c-In x Ga 1– x N films that have good epitaxial quality is difficult due to largely different lattice constants, , significantly different growth temperatures for the two binary compounds, and a lack of substrates for homoepitaxy. As a result, reports of the phase-pure growth of c-In x Ga 1– x N with more than 30% In content are scarce, and numerous works predict , and report − spinodal decomposition with the formation of an additional In-rich phase. In most cases, c-In x Ga 1– x N is heteroepitaxially grown on c-GaN.…”