Search

We present a detailed atomistic analysis of the electronic properties of m-plane InGaN/GaN quantum wells. The tight-binding model used treats realistically sized systems atomistically and accounts for compositional and structural inhomogeneities. Local variation in strain and built-in potential arising from random alloy fluctuations are explicitly included in the model. Many energy states of the supercells considered are calculated in order to determine the impact of the alloy fluctuations on the electronic structure of the system under investigation. We find that while the electrons are relatively insensitive to the local indium environment, the hole states are highly sensitive to it and are subject to very strong localization effects. These effects persist several states into the valence band. This strong localization of the hole states leads to a very broad distribution of ground state energies in different random configurations. Furthermore, we see that the localization leads to poor overlap between different hole states resulting in a reduced probability of transfer of carriers between different states. This feature should play an important role for transport properties in m-plane InGaN/GaN QWs. [ABSTRACT FROM AUTHOR]

In this paper we report on the impact that the quantum well growth temperature has on the internal quantum efficiency and carrier recombination dynamics of two sets of InGaN/GaN multiple quantum well samples, designed to emit at 460 and 530 nm, in which the indium content of the quantum wells within each sample set was maintained. Measurements of the internal quantum efficiency of each sample set showed a systematic variation, with quantum wells grown at a higher temperature exhibiting higher internal quantum efficiency and this variation was preserved at all excitation power densities. By investigating the carrier dynamics at both 10 K and 300 K we were able to attribute this change in internal quantum efficiency to a decrease in the non-radiative recombination rate as the QW growth temperature was increased which we attribute to a decrease in incorporation of the point defects. [ABSTRACT FROM AUTHOR]

The mechanisms governing efficiency droop in an In0.18Ga0.82N/GaN multiple quantum well structure were investigated using a combination of ultrafast time-resolved terahertz and photoluminescence spectroscopy. From excitation fluence dependent studies, a reduction in the room temperature photoluminescence efficiency to 3% of its maximum value was observed for an excitation fluence of 0.96 mJcm-2. A correlation was found between the onset of efficiency droop and the emergence of a peak on the high-energy side of the quantum well emission with a 1/e decay time of 19.6 ps. These characteristics were attributed to the saturation of localised states and the population of higher energy delocalised states. Time-resolved studies revealed different scaling behaviours between the terahertz and photoluminescence decay dynamics, suggesting that the saturation of localised hole states may be playing a part in the onset of efficiency droop. [ABSTRACT FROM AUTHOR]

Monolithic color synthesis is demonstrated using InGaN/GaN multiple quantum wells (QWs) grown on GaN microstripes formed by selective area epitaxy on SiO2 mask patterns. The striped microfacet structure is composed of (0001) and {11-22} planes, attributed to favorable surface polarity and surface energy. InGaN/GaN QWs on different microfacets contain spatially inhomogeneous compositions owing to the diffusion of adatoms among the facets. This unique property allows the microfacet QWs to emit blue light from the {11-22} plane and yellow light from the top (0001) plane, the mixing of which leads to the perception of white light emission. [ABSTRACT FROM AUTHOR]

We report exceptionally low thresholds (9.1 µJ/cm²) for room temperature lasing at ~450 nm in optically pumped Gallium Nitride (GaN) nanobeam cavity structures. The nanobeam cavity geometry provides high theoretical Q (>100 000) with small modal volume, leading to a high spontaneous emission factor, ß = 0.94. The active layer materials are Indium Gallium Nitride (InGaN) fragmented quantum wells (fQWs), a critical factor in achieving the low thresholds, which are an order-of-magnitude lower than obtainable with continuous QW active layers. We suggest that the extra confinement of photo-generated carriers for fQWs (compared to QWs) is responsible for the excellent performance. [ABSTRACT FROM AUTHOR]

Planar (In,Ga)N layers were grown on nanostripe arrays composed of InGaN/GaN multi quantum wells (MQWs) by metal–organic chemical vapor deposition. The MQW nanostripe arrays with height to width aspect ratios of about 0.5 and 1 were fabricated from planar coherently strained InGaN/GaN MQW samples. Independent of their aspect ratio, the nanostripes exhibited elastic relaxation perpendicular to the stripe direction after pattern fabrication, resulting in an a⊥ lattice constant perpendicular to the stripe direction larger than that of the GaN base layer. In a subsequent step, (In,Ga)N layers were grown on top of the nanostripe arrays, leading to the formation of planar films with a similar a⊥ lattice constant as the MQW stripes beneath. Bright luminescence was recorded from the planar, partially relaxed re-grown (In,Ga)N layers grown on the stripe arrays with an aspect ratio of 1. Plastic relaxation of the MQW stripes was observed after (In,Ga)N regrowth for samples with a stripe aspect ratio of 0.5, leading to luminescence quenching. [ABSTRACT FROM AUTHOR]