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BGaN epilayers with boron contents up to 5.6% were grown on SiC substrates by metal–organic chemical vapor deposition. The effects of boron incorporation on the structural and optical properties were studied by high‐resolution X‐ray diffraction (XRD), atomic force microscopy (AFM), Raman spectroscopy and photoluminescence (PL) spectroscopy. XRD reciprocal‐space maps around the symmetric 0002 and asymmetric reflections allowed evaluation of the lattice constants and lattice mismatch with respect to the underlying substrate. XRD rocking curves and AFM measurements indicated the mosaic microstructure of the epilayer. The impact of boron content on crystallite size, tilt and twist is evaluated and the correlation with threading dislocation density is discussed. The deterioration of optical properties with increasing boron content was assessed by Raman and PL spectroscopy. [ABSTRACT FROM AUTHOR]

The strain relaxation, surface morphology, and reflectivity of AlGaN‐distributed Bragg reflectors (DBRs) grown via metal–organic chemical vapor deposition on AlN/Al2O3 templates are investigated. Strain relaxation begins in a 10‐period Al0.50Ga0.50N (27 nm)/Al0.75Ga0.25N (29 nm) DBR, and the degree of strain relaxation (DSR) increases with the number of DBR periods. The 30‐period DBR exhibits a peak reflectivity of 0.82 at 279 nm, with a stopband of 12 nm. The DSR of n‐Al0.62Ga0.38N on the 30‐period DBR increases from 70% to 100% as the n‐Al0.62Ga0.38N thickness increases from 0.4 to 2.5 μm. Although the surface of a DBR comprises numerous spiral hillocks, n‐Al0.62Ga0.38N grown on an AlGaN DBR exhibits a step‐flow growth. A DSR of 100% with threading screw dislocations of 2.0 × 108 cm−2 and threading edge dislocations of 1.2 × 109 cm−2 is obtained for a 2.5 μm‐thick n‐Al0.62Ga0.38N on a 30‐period AlGaN DBR. [ABSTRACT FROM AUTHOR]

X‐ray diffraction from dislocation half‐loops consisting of a misfit segment with two threading arms extending from it to the surface is calculated by the Monte Carlo method. The diffraction profiles and reciprocal space maps are controlled by the ratio of the total lengths of the misfit and the threading segments of the half‐loops. A continuous transformation from the diffraction characteristic of misfit dislocations to that of threading dislocations with increasing thickness of epitaxial film is studied. Diffraction from dislocations with edge‐ and screw‐type threading arms is considered and the contributions of the two types of dislocations are compared. [ABSTRACT FROM AUTHOR]

Herein, the carrier lifetime in ≈5 × 1016 cm−3 n‐doped InxGa1−xAs layers is studied by diode current–voltage analysis and by time‐resolved photoluminescence. Two sets of hetero‐epitaxial layers are grown on semi‐insulating InP or GaAs substrates. The first set corresponds with a constant In content p + n stack, while the second set has a fixed x = 0.53 for the n‐layer, while containing various extended defect densities by using a strain relaxed buffer with different x. This results in threading dislocation densities (TDDs) between ≈105 cm−2 and a few 109 cm−2. It is shown that the overall trend of the recombination lifetime versus TDD can be described by a first‐order model considering a finite recombination lifetime value inside a dislocation core of 1 nm. For the generation lifetime, a strong electric‐field enhancement factor is found. Also, the residual strain in the n‐layer has an impact. Overall, the safe limit for TDD depends on the type of application and on the operation conditions (reverse diode bias). [ABSTRACT FROM AUTHOR]

Threading dislocations in c‐plane (Al,Ga)N layers are surrounded by areas with reduced light generation efficiency, called "dark spots." These areas are observable in luminescence measurements with spatial resolution in the submicrometer range. Dark spots reduce the internal quantum efficiency in single layers and light‐emitting devices. In cathodoluminescence measurements, the diameter of dark spots (full width at half maximum [FWHM]) is observed to be 200–250 nm for GaN. It decreases by 30–60% for AlxGa1−xN with x ≈ 0.5. Furthermore, the dark spot diameter increases with increasing temperature from 83 to 300 K in AlGaN, whereas it decreases in GaN. Emission energy mappings around dark spots become less smooth and show sharper features on submicrometer scales at low temperature for AlGaN and, on the contrary, at high temperature for GaN. It is concluded that charge carrier localization dominates the temperature dependence of dark spot diameters and of the emission energy distribution around threading dislocations in AlGaN, whereas the temperature‐dependent excitation volume in cathodoluminescence and charge carrier diffusion limited by phonon scattering are the dominant effects in GaN. Consequently, with increasing temperature, nonradiative recombination related to threading dislocations extends to wider regions in AlGaN, whereas it becomes spatially limited in GaN. [ABSTRACT FROM AUTHOR]

Heteroepitaxial crystalline films underlie many electronic and optical technologies but are prone to forming defects at their heterointerfaces. Atomic‐scale defects such as threading dislocations that propagate into a film impede the flow of charge carriers and light degrading electrical/optical performance of devices. Diagnosis of subsurface defects traditionally requires time‐consuming invasive techniques such as cross‐sectional transmission electron microscopy. Using III–V films grown on Si, noninvasive, bench‐top diagnosis of subsurface defects have been demonstrated by optical second‐harmonic scanning probe microscope. A high‐contrast pattern is observed of subwavelength "hot spots" caused by scattering and localization of fundamental light by defect scattering sites. Size of these observed hotspots are strongly correlated to the density of dislocation defects. The results not only demonstrate a global and versatile method for diagnosing subsurface scattering sites but uniquely elucidate optical properties of disordered media. An extension to third harmonics would enable irregularities detection in non‐χ(2) materials making the technique universally applicable. [ABSTRACT FROM AUTHOR]

Residual contrast of threading edge dislocations is observed in synchrotron back‐reflection X‐ray topographs of 4H‐SiC epitaxial wafers recorded using basal plane reflections where both g · b = 0 and g · b × l = 0. The ray‐tracing simulation method based on the orientation contrast formation mechanism is applied to simulate images of such dislocations by applying surface relaxation effects. The simulated contrast features match the observed features on X‐ray topographs, clearly demonstrating that the contrast is dominated by surface relaxation. Depth profiling indicates that the surface relaxation primarily takes place within a depth of 5 µm below the surface. [ABSTRACT FROM AUTHOR]

Threading dislocations (TDs) in the GaN substrate and homoepitaxial layer are nondestructively evaluated using X‐ray topography (XRT), Raman spectroscopy, and multiphoton photoluminescence (MPPL) imaging. When the XRT and Raman mapping images are compared, TDs in the GaN substrate are identified as threading edge dislocations (TEDs), threading mixed dislocations (TMDs), and threading screw dislocations (TSDs). TDs are observed to propagate from the GaN substrate to the epitaxial layer. From MPPL imaging, the TEDs are found to be inclined in the [11¯00] direction, which is at 90° from the Burgers vector. The TMD studied in detail is found to be inclined in the [1¯21¯0] direction, which is parallel to the Burgers vector. The feasibility of identifying TDs via analysis of the inclined direction of the dislocations in the GaN epitaxial layer is suggested. [ABSTRACT FROM AUTHOR]

X‐Ray diffraction microstrain characterization is a technique which enables the quantification of threading dislocations by measuring the radial microstrain field surrounding these defects. This work demonstrates how to accurately perform these measurements on a broad range of GaN samples. In particular, for GaN grown on Si substrates with large stress gradient through the layer, the measurements need to be performed on the (20–25) reflection to avoid being affected by a macrostrain influence. A comparison of this characterization with cathodoluminescence and X‐ray diffraction lattice misorientations measurements shows differences in the measurement depth, so the results are affected by the various evolutions of dislocations densities through the layers of the different samples. Independently of the measurement depth, the analysis also highlights a dependence of the X‐ray measurements results on the type of sample, in particular the starting substrate. Microstrain measurements appear therefore as being well suited for the comparison of threading dislocations densities between similar GaN layers. It can be used to replace lattice misorientations measurements, or be associated with them to obtain an edge versus screw dislocations ratio. [ABSTRACT FROM AUTHOR]

The growth mechanism of V‐defects in GaN films was investigated. It was observed that the crystal faces of both the sidewall of a V‐defect and the sidewall of the GaN film boundary belong to the same plane family of , which suggests that the formation of the V‐defect is a direct consequence of spontaneous growth like that of the boundary facet. However, the growth rate of the V‐defect sidewall is much faster than that of the boundary facet when the V‐defect is filling up, implying that lateral growth of planes is not the direct cause of the change in size of V‐defects. Since V‐defects originate from dislocations, an idea was proposed to correlate the growth of V‐defects with the presence of dislocations. Specifically, the change in size of the V‐defect is determined by the growth rate around dislocations and the growth rate around dislocations is determined by the growth conditions. [ABSTRACT FROM AUTHOR]

Boron‐doped diamond epilayers grown over diamond substrates have a different lattice parameter from the undoped diamond substrate, which introduces a lattice mismatch between substrates and epilayers. This can generate misfit dislocations at the interface when the epilayer reaches a certain critical thickness. For a boron concentration of about 1 × 1020 atoms cm−3, the calculated lattice mismatch is about 1.3 × 10−4 and the critical thickness is of the order of 0.2 µm. In the epilayers studied, grown over high‐pressure high‐temperature 1b (001) substrates, the lattice mismatch and the epilayer thickness are 1.3 × 10−4, 30 µm and 6.5 × 10−4, 4 µm. The epitaxial strain has been relaxed by the generation of two orthogonal misfit dislocation systems. These are edge dislocations parallel to the [100] and [010] directions with a Burgers vector making an angle of 45° with the (001) interface. Their lengths are 40–60 µm and their lineal densities 200–240 cm−1. They are heterogeneously nucleated, propagated in the form of half‐loops along the slip planes (011) and (101), respectively, and related mainly to ⟨111⟩ threading dislocations emerging from octahedral growth sectors. Another kind of half‐loop originates from the substrate growth sector boundaries. Limited X‐ray topography has been demonstrated to be a very useful tool to discriminate between substrate and epilayer defects when their lattice mismatch is not sufficient to separate such defects in conventional Lang topography. X‐ray section topography has confirmed the presence of [001] dislocations in the epilayers and the misfit half‐loops related to threading dislocations propagating from the interface. Limited X‐ray and section topography have been used to characterize defects in both boron‐doped homoepitaxial films and high‐pressure high‐temperature 1b (001) diamond substrates. Lattice mismatch generates, at the interface, two orthogonal systems of misfit dislocations in the form of half‐loops propagating from the interface defects, particularly threading dislocations and growth sector boundaries. [ABSTRACT FROM AUTHOR]

A gallium nitride (GaN) epitaxial layer with a low density of threading dislocations is successfully grown on a silicon substrate by using in situ gas etching. Silicon nitride (SiNx) film is used as a mask, and ammonia is intermittently supplied in hydrogen ambient during the etching. After etching, high‐density deep pits appeared on the surface of a GaN template layer and corresponded to the threading dislocations in the layer. In this novel method, before growing an additional GaN layer on the template GaN layer, a second SiNx layer is deposited after the etching process, and this layer prevents GaN nuclei from growing on the upper side‐walls of the pits. By using this method, the density of threading dislocations of the GaN surface is reduced to 6.7 × 107 cm−2. This method is cost effective, completing all the necessary processes in one growth run without taking samples out from a metalorganic chemical vapor deposition (MOCVD) reactor. [ABSTRACT FROM AUTHOR]

Abstract: In this contribution, the correlation between the microstructure of thin gallium nitride films and the ammonia flow applied during their growth by high‐temperature vapor phase epitaxy is described. The films were grown directly on (001)‐oriented sapphire substrates. Their microstructure was investigated using high‐resolution X‐ray diffraction, electron microscopy and micro‐Raman spectroscopy. The ammonia flow was found to affect the residual stress, the density of threading dislocations, the density of basal‐plane stacking faults and the density of inversion domain boundaries. It is shown that the ammonia flow is an important parameter of the deposition process that can be used to reduce concurrently the residual stress and the density of microstructure defects. [ABSTRACT FROM AUTHOR]

Diamond lateral growth is a useful technique to assess 3D architectures of devices. The requirement of the overgrowth on etched substrates has been observed to have additional benefit in the crystallinity of the diamond. The surface roughness is enhanced and threading dislocation density is reduced as a consequence of the lateral growth on patterned substrates. Under these premises, this contribution presents a study of defects and terrace coalescences for the lateral growth on a trenched surface substrates with different trench widths. The latter was achieved on 100-oriented HPHT diamond substrates grown by MPCVD and using very thin-doped layers to mark the growth plane every 100 nm. The results showed high density of threading dislocations that were gathered to the centre of the coalescence. These threading dislocations, as well as planar defects, were investigated using transmission electron microscopy. The mechanism of those defects generation and the better conditions to achieve defect-free areas are discussed. [ABSTRACT FROM AUTHOR]

The effects of atomic arrangements of group-III elements on the electronic structures of threading dislocations in III-nitride semiconductors are theoretically investigated on the basis of first-principles calculations within the density functional theory. Our calculations for edge and screw dislocations in Al [ABSTRACT FROM AUTHOR]

Semipolar orientations of GaN have attracted considerable attention as potential platforms for high brightness light-emitting devices. The heteroepitaxy of semipolar GaN layers results in high densities of threading dislocations (TDs) and basal-plane stacking faults (BSFs). Various defect reduction methods have been employed to improve the crystal quality of the semipolar substrates, among which the in situ epitaxial lateral overgrowth (ELO) is of great importance due to its relatively simple procedure, low cost, and high effectiveness in reducing density of TDs. We have shown that in situ deposited nano-porous SiN x could act as a blocking layer preventing both TDs and BSFs from penetrating to overgrown semipolar [ABSTRACT FROM AUTHOR]

The microstructure of polar GaN layers, grown by upgraded high-temperature vapour phase epitaxy on [001]-oriented sapphire substrates, was studied by means of high-resolution X-ray diffraction and transmission electron microscopy. Systematic differences between reciprocal-space maps measured by X-ray diffraction and those which were simulated for different densities of threading dislocations revealed that threading dislocations are not the only microstructure defect in these GaN layers. Conventional dark-field transmission electron microscopy and convergent-beam electron diffraction detected vertical inversion domains as an additional microstructure feature. On a series of polar GaN layers with different proportions of threading dislocations and inversion domain boundaries, this contribution illustrates the capability and limitations of coplanar reciprocal-space mapping by X-ray diffraction to distinguish between these microstructure features. [ABSTRACT FROM AUTHOR]

In order to achieve high breakdown voltage in GaN vertical power devices, low threading dislocation density and low background carrier concentration is required. This work demonstrates a decrease in the background carrier concentration and threading dislocation density (TDD) with an increase in the thickness of un-intentionally doped (UID) GaN grown on sapphire. p-n diodes grown and fabricated on this epi, using 4.8 µm UID GaN, showed a breakdown voltage of 730 V, breakdown field of 1.75 MV cm−1 and an on-resistance of 5.1 m Ω cm2. The figure of merit (FOM), VBR2/ RON, thus obtained is approximately 105 MW cm−2. This is the highest reported FOM value for p-n diodes on GaN on sapphire or Si. Lowering the carrier concentration and dislocation density is thus shown to be critical for achieving high breakdown voltages on GaN on sapphire. [ABSTRACT FROM AUTHOR]

We have carried out atomistic simulations, based on density functional theory, to investigate the atomic and electronic structures of the three types of prismatic threading dislocations in hexagonal gallium nitride. Screw and mixed threading dislocations were demonstrated to introduce both deep and shallow gap states, while most of core configurations of the edge dislocation introduce solely shallow states. The higher electrical activity of both screw and mixed dislocations, compared to the edge one, is correlated with the high dispersion of their energy levels, within the GaN bandgap. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

It is demonstrated in this paper that 1.9-mm-thick gallium nitride grown by Hydride Vapor Phase Epitaxy (HVPE) on an ammonothermally grown GaN seed can reproduce the structural, in terms of defects, properties of the seed. The etch pit density and its correlation to the threading dislocation density in the ammonothermal GaN substrate and the HVPE-GaN layer is presented and analyzed. However, it has recently been observed that for HVPE-GaN thicker than 2 mm some additional defects are formed in the new grown material. Therefore, three HVPE growth runs were performed in the same experimental conditions, using three structurally identical ammonothermally grown GaN seeds of different thicknesses. The influence of the thickness of the seeds on the crystallization process and the properties of the HVPE-GaN layers is shown and discussed. [ABSTRACT FROM AUTHOR]

Despite the recent progress in gallium nitride (GaN) growth technology, the excessively high threading dislocation (TD) density within the GaN crystal, caused by the reliance on heterogeneous substrates, impedes the development of high-efficiency, low-cost, GaN-based heterostructure devices. For the first time, the chemical exfoliation of completely TD-free, single-crystalline, ultrathin (tens of nanometers) GaN nanomembranes is demonstrated using UV-assisted electroless chemical etching. These nanomembranes can act as seeding layers for subsequent overgrowth of high-quality GaN. A model is proposed, based on scanning and transmission electron microscopy as well as optical measurements to explain the physical processes behind the formation of the GaN nanomembranes. These novel nanomembranes, once transferred to other substrates, present a unique and technologically attractive path towards integrating high-efficiency GaN optical components along with silicon electronics. Interestingly, due to their nanoscale thickness and macroscopic sizes, these nanomembranes may enable the production of flexible GaN-based optoelectronics. [ABSTRACT FROM AUTHOR]

A new method of determining the piezoelectric field around dislocations from high-resolution transmission electron microscopy images is presented. In order to determine the electrical potential distribution near a dislocation core, we used the distortion field, obtained using the geometrical phase method and the non-linear finite element method. The electrical field distribution was determined taking into account the inhomogeneous strain distribution, finite geometry of the sample and the full couplings between elastic and electrical fields. The results of the calculation for a transmission electron microscopy thin sample are presented. [ABSTRACT FROM AUTHOR]

An error in the article by Gao, Zhang, Zhu, Wu, Mo, Pan, Liu & Jiang [J. Appl. Cryst. (2019), 52, 637–642] is corrected. [ABSTRACT FROM AUTHOR]

Epitaxial growth of polar GaN is frequently made on AlN/Si substrates that contain a large density of threading dislocations induced by the mismatch of their lattice parameters and thermal expansion coefficients. In this paper, the structural and electrical properties of surface and extended defects found in 220 nm {0001} AlN films grown epitaxially on {111} oriented Si substrate by metalorganic chemical vapor deposition are characterized. Three types of surface depressions are recognized by atomic force microscopy (AFM) that correspond to V‐defects and their clusters and individual threading dislocations. Transmission electron microscopy studies prove that all V‐defects are attached to threading screw or mixed‐type threading dislocations. The electrical activity of the defects in the AlN film is assessed by measuring the electron beam induced current (EBIC) across Au/Ni/AlN Schottky barrier. The largest drop of EBIC compared to defect‐free regions is observed at clusters of V‐defects, which have a low density of (2.4 ± 0.4) × 107 cm−2. Only a very weak drop of EBIC is found at isolated threading dislocations, which have much higher density compared to clusters of V‐defects. Considering the defects studied, the electrical properties of AlN films are primarily affected by threading dislocations, despite the relatively weak recombination efficiency of individual dislocations. [ABSTRACT FROM AUTHOR]

High‐quality GaN film is grown on graphene with the underneath sputtered AlN modified layer using metal organic chemical vapor deposition. Due to the modulation effect of sputtered AlN on the surface potential and the chemical reactivity of graphene, the nucleation probability of GaN is significantly improved. The GaN epitaxial layer shows excellent crystal quality and surface morphology, and has very low threading dislocation density of 1.78 × 108 cm−2. Furthermore, the mechanism of threading dislocation suppression is revealed according to the transmission electron microscope results. The improved nucleation probability and enhanced lateral growth mode lead to the formation of short‐range stacking faults in c‐plane GaN, which block the propagation of threading dislocations along the growth direction. Moreover, the formation and evolution mechanism of the short‐range stacking faults are discussed. The results in this work not only offer a promising approach to propel the widespread application of GaN on graphene, but also provide a new idea for the regulation and suppression of defects in the growth of nitride semiconductors. [ABSTRACT FROM AUTHOR]

Through UV‐assisted electroless chemical etching, single crystalline gallium nitride nanomembranes are exfoliated by B. S. Ooi and co‐workers on page 2305, with the threading‐dislocation cores selectively detached. This false‐color scanning electron microscope image shows the nanomembrane lying on top of porous gallium nitride. The enlarged region reveals the gallium nitride nanowires (green), formed from threading‐dislocations cores, protruding through the gallium nitride nanomembrane. [ABSTRACT FROM AUTHOR]