Evolution of the mosaic structure in InGaN layer grown on a thick GaN template and sapphire substrate (original) (raw)
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Structural analysis of an InGaN/GaN based light emitting diode by X-ray diffraction
Journal of Materials Science-materials in Electronics, 2010
The important structural characteristics of hexagonal GaN in an InGaN/GaN multi quantum well, which was aimed to make a light emitted diode and was grown by metalorganic chemical vapor deposition on c-plain sapphire, are determined by using nondestructive high-resolution X-ray diffraction in detail. The distorted GaN layers were described as mosaic crystals characterized by vertical and lateral coherence lengths, a mean tilt, twist, screw and edge type threading dislocation densities. The rocking curves of symmetric (00.l) reflections were used to determine the tilt angle, while the twist angle was an extrapolated grown ω-scan for an asymmetric (hk.l) Bragg reflection with an h or k nonzero. Moreover, it is an important result that the mosaic structure was analyzed from a different (10.l) crystal direction that was the angular inclined plane to the z-axis. The mosaic structure parameters were obtained in an approximately defined ratio depending on the inclination or polar angle of the sample.
Japanese Journal of Applied Physics, 2012
The accurate alloy composition of a nonpolar InGaN grown on m-plane GaN is estimated from X-ray reciprocal-space maps (RSMs) of (20 21) and (21 30) diffractions. In this estimation, the anisotropic residual strain in m-plane is carefully considered. In order to avoide the error which may be generated by the anisotropic strain and tilted domains in the film of InGaN, the lattice constants along m-, a-, and c-directions are determined using a pair of two RSMs normalized to the unit reciprocal vector along m-direction. The indium content of InGaN is derived from RSMs data using Poisson effect and Vegard's law. Based on this method, the incorporation of indium into InGaN is investigated. This incorporation is found to be promoted with the increase in the substrate miscut angle and the growth rate. From the precise analysis of RSMs, some of the InGaN domains on m-plane GaN substrates are found to be tilted toward AEa-direction despite of the substrate miscut toward c-direction.
Investigation of structural, optical and morphological properties of InGaN/GaN structure
Applied Physics A, 2018
In this study, InGaN/GaN structure is investigated in the temperature range of 300-500 °C with steps of 50 °C. InGaN/ GaN multi-quantum well structure is deposited on c-orientated sapphire wafer by metal organic chemical vapour deposition method. All the parameters except for temperature kept constant during growth period. InGaN/GaN structures with different In content are investigated by XRD technique. Their structural, optical and morphological characteristics are determined by high resolution X-ray diffraction, Fourier transform spectroscopy (FTIR), photo luminescence (PL), transmission and atomic force microscopy (AFM). According to FTIR and PL spectra's, it is noticed that band gap values coincide with blue region in the electromagnetic spectrum. As a result of transmission measurements it is seen that light is completely absorbed by the sample at approximately 390 nm. Using XRD technique, dislocation densities and strain are calculated. Full width at half maximum of the XRD peak values gained from X-ray diffraction are used in an alternative method called Williamson-Hall (W-H). Using W-H method, lateral and vertical crystal lengths and tilt angles are determined. Surface roughness parameters are investigated by AFM. Different properties of GaN and InGaN layers are compared as dependent on increasing temperature. According to AFM images it is seen that these structures have high surface roughness and large crystal size. All the results yielded from the mentioned methods are in good agreement with the previous works done by different authors.
Mosaicity of GaN Epitaxial Layers: Simulation and Experiment
physica status solidi (b), 2001
High-resolution X-ray diffraction has been used to analyze GaN epilayers with varying coalescence thickness which were grown by MOVPE on (0001) oriented sapphire. The decrease of the density of edge type threading dislocations with increasing coalescence thickness causes a marked difference in the mosaicity of the samples. As the defects form along the grain boundaries, this corresponds to an increase in lateral coherence length with increasing coalescence thickness. The lateral coherence length has been obtained from simulations of reciprocal lattice points of off-axis Bragg reflections, measured in asymmetric diffraction geometry.
Japanese Journal of Applied Physics, 2013
The growth of InGaN with intermediate In compositions on GaN/sapphire template and AlN/Si(111) substrate has been comparatively studied. By using an metalorganic vapor phase epitaxy (MOVPE) system with a horizontal reactor, InGaN films are grown at a temperature of 600-800 C in the pressure of 150 Torr. By optimizing growth temperature and trimethylindium=ðtrimethylindium þ triethylgalliumÞ molar ratio, single crystalline In x Ga 1Àx N with x ¼ 0{1 are successfully grown on both substrates. The films grown at a relatively high temperature (!700 C) with In compositions of 0.3 or less show phase separation when their thickness exceeds a critical value (0.25-0.4 m), while the samples grown at 600 C with In compositions of 0.35-0.5 show no phase separation even if the thickness is increased to 0.7 m. To evaluate the crystalline quality of grown films, FWHM of X-ray rocking curve (XRC) for InGaN(0002), tilt, is measured. There is no marked difference in tilt data between films grown on GaN/-Al 2 O 3 (0001) and AlN/Si(111). For the samples grown at 600 C with In contents of 0.35-0.5, tilt data are drastically increased and widely scattered suggesting the existence of important unknown parameters that govern crystalline quality of InGaN grown at a relatively low temperature.
Strain relaxation in graded InGaN/GaN epilayers grown on sapphire
Applied Physics Letters, 2003
Graded InGaN buffers were employed to relax the strain arising from the lattice and thermal mismatch in GaN/InGaN epilayers grown on sapphire. An enhanced strain relaxation was observed in GaN grown on a stack of five InGaN layers, each 200 nm thick with the In content increased in each layer, and with an intermediate thin GaN layer, 10 nm thick inserted between the InGaN layers, as compared to the conventional two-step growth of GaN epilayer on sapphire. The function of the intermediate layer is to progressively relax the strain that builds up in the InGaN layer. If the InGaN layers were graded too rapidly, more dislocations will be generated. This increases the probability of the dislocations getting entangled, thereby impeding the motion of the dislocations to relax the strain in the InGaN layer. The optimum growth conditions of the intermediate layer play a major role in promoting the suppression and filling of the V-pits in the GaN cap layer, and were empirically found to be a thin 10-nm GaN layer grown at 750°C and annealed at 1000°C.
Characteristics of the surface microstructures in thick InGaN layers on GaN
Optical Materials Express, 2013
This paper focuses on a comparative study of optical, morphological, microstructural and microcompositional properties of typical InGaN samples which exhibit V-defects but also two additional surface defects features, referred to as inclusion#1 (Ic1) and inclusion#2 (Ic2). HR-XRD, AFM, SEM, STEM and EDX are used to characterize such defects. Furthermore, hyperspectral mapping, spot mode and depth-resolved CL measurements provided useful informations on the optical emission properties and microstructure. The main characteristic of Ic1 luminescence peak is a decrease in intensity and no obvious shift in the CL peak position when going from the outside to the middle of such defect. More interesting was Ic2 which is shown to be local 3D top surface In-rich InGaN domains embedded in an homogeneous InGaN matrix. In fact, this study pointed out that close to the interface GaN/InGaN, it exists a 30 nm thick fully strained InGaN layer with constant indium incorporation. As the growth proceeds spatial fluctuation of the In content is observed and local In-rich 3D domains are shown to emerge systematically around threading dislocations terminations.
Graded InGaN Buffers for Strain Relaxation in GaN/InGaN Epliayers Grown on Sapphire
Graded InGaN buffers are employed to relax the strain arising from the lattice and thermal mismatches between GaN/InGaN epilayers grown on sapphire. The formation of V-pits in linearly graded InGaN/GaN bulk epilayers is illustrated. The V-pits were sampled using Atomic Force Microscopy and Scanning Electron Microscopy to examine their variation from the theoretical geometry shape. We discovered that the size of the V-pit opening in linearly graded InGaN, with and without GaN cap layer, has a Gaussian distribution. As such, we deduce that the V-pits are produced at different rates, as the growth of the InGaN layer progresses. In Stage I, the V-pits form at a slow rate at the beginning and then accelerate in Stage II when a critical thickness is reached before decelerating in Stage III after arriving at a mean size. It is possible to fill the V-pits by growing a GaN cap layer. It turns out that the filling of the V-pits is more effective at lower growth temperature of the GaN cap layer and the size of the V-pits opening, which is continued in to GaN cap layer, is not dependent on the GaN cap layer thickness. Furthermore, graded InGaN/GaN layers display better strain relaxation as compared to conventionally grown bulk GaN. By employing a specially design configuration, the V-pits can be eliminated from the InGaN epilayer.
Microstructural characterization of InGaN/GaN multiple quantum wells with high indium composition
Journal of Crystal Growth, 2001
The microstructural study of InGaN/GaN multiple quantum well (MQW) structures with high In (indium) composition (>30%) has been performed using transmission electron microscopy (TEM). The increased strain in InGaN/GaN MQWs by high In composition is relaxed by the formation of several defects such as dislocations, stacking faults, V-defects, and tetragonal shape defects. High-resolution TEM (HRTEM) measurement shows a new formation mechanism of V-defects, which is related to the stacking mismatch boundary induced by stacking faults. These Vdefects result in different growth rates of the GaN barriers according to the degree of the bending of InGaN well layers, which changes the period thickness of the superlattice. In addition, evidence of In clustering is directly observed both by using an In ratio map of the MQWs and from In composition measurements along an InGaN well using energy filtered TEM (EFTEM). r
Journal of the Korean Physical Society, 2012
Transmission electron microscopy (TEM) was used to survey the microstructures of InGaN/GaN epitaxial layers deposited on c-plane sapphire substrates by using the metalorganic chemical vapor deposition (MOCVD) technique. Pt nanoclusters were deposited at the InGaN/GaN epitaxial layer/sapphire substrate (sample A) interface and under the multi-quantum-well (MQW) layers (sample B), aiming at understanding the effect of the Pt nanoclusters on the microstructural characteristics of the epitaxial layers. Experimental results showed that the growth of the epitaxial layer in sample A was much better than that in sample B. The dislocation densities were measured as ∼10 7 cm −2 and ∼10 8 cm −2 in sample A and sample B, respectively. The lower dislocation density in sample A was due to threading dislocations (TDs) being stopped by the nanoclusters at the interface. For MQWs in light-emitting layers, the interfaces between the InGaN and the GaN barriers in sample A were very obvious and straight whereas those in sample B were not.