InGaN quantum wells have been found to be extremely sensitive exposure the electron beam in transmission microscope (TEM). High-resolution TEM images acquired immediately after first irradiating a region of well indicates no gross fluctuations indium content alloy. During only brief period irradiation, inhomogeneous strain is introduced material due damage. This very similar that expected from genuine nanometer-scale composition which suggests there possibility falsely detecting indium-rich...

A novel soft-solution technique is used to grow epitaxial Zn0.98Co0.02O films on the c-plane (0001) of a single-crystal sapphire substrate. Annealing in precisely controlled atmospheres shows that ferromagnetism not linked carrier-concentration density. Undertaking cyclic annealing studies presence or absence Zn vapor (see figure) interstitials but oxygen vacancies are critical defects for inducing ferromagnetism.

We have studied the low-temperature (T=6K) optical properties of a series InGaN∕GaN single-quantum-well structures with varying indium fractions. With increasing fraction peak emission moves to lower energy and strength exciton–longitudinal-optical (LO)-phonon coupling increases. The Huang–Rhys factor extracted from Fabry–Pérot interference-free photoluminescence spectra has been compared results model calculation, yielding value approximately 2nm for in-plane localization length scale...

Localization lengths of the electrons and holes in InGaN/GaN quantum wells have been calculated using numerical solutions effective mass Schr\"odinger equation. We treated distribution indium atoms as random found that resultant fluctuations alloy concentration can localize carriers. By a locally varying function we contribution to potential energy carriers from band gap fluctuations, deformation potential, spontaneous piezoelectric fields. considered effect well width these contribute...

An InxGa1−xN∕GaN multiple quantum well (MQW) structure that exhibited bright photoluminescence was examined with the three-dimensional atom probe. The wells were clearly imaged and indium fraction x measured to be 0.19±0.01, in good agreement x-ray diffraction measurements. distribution of MQWs analyzed: no evidence for either high concentration regions or clustering found, contrast many transmission electron microscopy studies literature. authors conclude is not necessary luminescence InGaN.

There is a great deal of interest in the underlying causes efficiency droop InGaN/GaN quantum well light emitting diodes, with several physical mechanisms being put forward to explain phenomenon. In this paper we report on observation reduction localization induced S-shape temperature dependence peak photoluminescence energy increasing excitation power density. This key fingerprint carrier localization. Over range density where depth S shape reduced, also observe integrated intensity per...

We describe the growth of InGaN quantum dots (QDs) by metalorganic vapor phase epitaxy. A thin epilayer is grown on a GaN buffer layer and then annealed at temperature in molecular nitrogen inducing dot formation. Microphotoluminescence studies these QDs reveal sharp peaks with typical linewidths ∼700 μeV 4.2 K, linewidth being limited spectral resolution. Time-resolved photoluminescence suggests that excitons structures have lifetimes excess 2 ns K.

A series of GaN films were grown by metalorganic vapor phase epitaxy on nitrided sapphire using an initial annealed low-temperature nucleation layer (LT-NL), without employing any conventional threading dislocation (TD) reduction methods. Film thicknesses ranging from the LT-NL to 500 nm used. The island network morphology was investigated at each growth stage atomic force microscopy. Data cathodoluminescence studies showed initially uniform luminescence, followed gradual development bright...

The critical thickness gives the transition point between fully strained and relaxed heteroepitaxial films determines onset of defect generation, including misfit dislocations, cracks, V-pits. An important variable in calculations concerning dislocations is dislocation energy. It consists two contributions: elastic energy bulk material around a core. latter part often neglected. Recent atomistic have estimated this quantity together with radius cores wurtzite III-nitrides. effect core on...

In a wide variety of InGaN/GaN quantum well (QW) structures, defects are observed which consist trench partially or fully enclosing region the QW having altered emission properties. For various different defect morphologies, cathodoluminescence studies suggest that is redshifted in enclosed region. Based on transmission electron microscopy and atomic force data, we sub-surface structure consists basal plane stacking fault bounded by mismatch boundary, terminates at apex V-shaped trench.

In this paper, we compare and contrast the experimental data theoretical predictions of low temperature optical properties polar nonpolar InGaN/GaN quantum well structures. both types structure, at temperatures are governed by effects carrier localisation. structures, effect in-built electric field leads to electrons being mainly localised width fluctuations, whereas holes regions within wells, where random distribution local minima in potential energy. This a system independently holes....

InGaN-based light emitting diodes and multiple quantum wells designed to emit in the green spectral region exhibit, general, lower internal efficiencies than their blue-emitting counter parts, a phenomenon referred as “green gap.” One of main differences between green-emitting samples is that well growth temperature for structures at longer wavelengths, order reduce effects In desorption. this paper, we report on impact optical properties InGaN/GaN 460 nm 530 nm. It was found both sets...

We have determined the indium content and layer thicknesses in an InGaN epilayer InGaN/GaN quantum well structures by high-resolution x-ray diffraction (XRD) using (002) reflection. The thickness of total repeat (an plus a GaN barrier) superlattice is easily from spacing between satellite peaks omega/2theta scan. Measurement individual layers less straightforward, since for multilayer peak positions are influenced both ratio to layer. Thus, several different models may give reasonable fits...

Pulsed light–current characteristics of InGaN/GaN quantum well light-emitting diodes have been measured as a function temperature, with sublinear behavior observed over the whole temperature range, 130–330 K. A distinctive dependence is also noted where light output, at fixed current, initially increases before reaching maximum 250 K and then decreases subsequent in temperature. On basis drift diffusion model, we can explain by influence large acceptor ionization energy Mg-doped GaN together...

The morphology of InGaN epilayers grown by metal-organic vapor phase epitaxy on GaN pseudosubstrates has been examined atomic force microscopy. composition the measured using a combination secondary ion mass spectrometry and x-ray photoelectron spectroscopy. dependence growth mode conditions investigated. At lowest temperatures NH3 fluxes, two-dimensional island nucleation is described, in which flat islands form stacks align along underlying terraces. As temperature increased transition to...

We have studied a series of GaN films grown with range dislocation densities by atomic force microscopy (AFM), transmission electron (TEM) and high resolution x-ray diffraction (HRXRD). The (002), (004), (006), (105), (204), (302), (100), (110), (200) (300) reflections were measured as reciprocal space maps (RSMs) or scans in ω ω/2θ. latter 4 in-plane using low, glancing, incident angle respect to the film surface. used variety different methods try obtain reliable measurements for mosaic...

The three-dimensional atom probe has been used to characterize green- and blue-emitting InxGa1−xN∕GaN multiple quantum well structures with subnanometer resolution over a 100nm field of view. distribution indium in InxGa1−xN samples different compositions is analyzed. No evidence found wherein the deviates from that random alloy, which appears preclude clustering as cause reported carrier localization these structures. upper interface each layer shown be rougher more diffuse than lower...

The startling success of GaN-based light emitting diodes despite the high density dislocations found in typical heteroepitaxial material has been attributed to localization carriers at non-uniformities quantum wells (QWs) which form active region such devices. Here, we review different possible structures within QWs could act as sites, length scales ranging from atomic tens nanometre range. In some several mechanisms be operational, but challenge remains optimize QWs' structure achieve...

Gross well-width fluctuations have been observed by transmission electron microscopy (TEM) in single InGaN∕GaN quantum wells (QWs) grown metal-organic vapor phase epitaxy. Similar thickness variations are commercial, green multi-QW light emitting diodes. Atomic force studies of equivalent epilayers suggest that these arise from a network interlinking InGaN strips, which found (using TEM) to be indium rich at their centers. Plan-view TEM indicates 90±8% all threading dislocations (TDs)...

InGaN-based active layers within microcavity resonators offer the potential of low threshold lasers in blue spectral range. Here, we demonstrate optically pumped, room temperature lasing high quality factor GaN microdisk cavities, containing InGaN quantum dots (QDs) with thresholds as 0.28 mJ/cm2. The demonstration action from cavities QDs layer, provides a critical step for nitrides realizing photonic devices efficient coupling between and an optical cavity

The impact of trench defects in blue InGaN/GaN light emitting diodes (LEDs) has been investigated. Two mechanisms responsible for the structural degradation multiple quantum well (MQW) active region were identified. It was found that during growth p-type GaN capping layer, loss part enclosed within a defect occurred, affecting top-most QWs MQW stack. Indium platelets and voids also to form preferentially at bottom presence high densities LEDs relate significant reduction photoluminescence...

Dislocations in undoped GaN move response to the in-plane tensile stress present during film growth. Dislocation movement growth relieves stress, produces arrays of a-type dislocations and reduces overall dislocation density, with preferential reduction (a+c)-type dislocations. However, Si-doping limits movement, limiting relief that develops reduction, probably due formation Si impurity atmospheres at Consequently, Si-doped films are under relatively greater compared grown similar...