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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 structural properties of lattice-matched InAlAs/InP layers grown by molecular beam epitaxy have been studied using atomic force microscopy, scanning electron microscopy and micro-photoluminescence spectroscopy. The formation of the surface pits with lateral sizes in the micron range and a depth of about 2 ÷ 10 nm has been detected. The InP substrate annealing temperature and value of InAlAs alloy composition deviation from the lattice-matched InxAl1−xAs/InP case (x = 0.52) control the density of pits ranging from 5 × 105 cm−2 ÷ 108 cm−2. The pit sizes are controlled by the InAlAs layer thickness and growth temperature. The correlation between the surface pits and threading dislocations has been detected. Moreover, the InAlAs surface is characterized by composition inhomogeneity with a magnitude of 0.7% with the cluster lateral sizes and density close to these parameters for surface pits. The experimental data allow us to suggest a model where the formation of surface pits and composition clusters is caused by the influence of a local strain field in the threading dislocation core vicinity on In adatoms incorporating kinetic. [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]

Heteroepitaxial growth of high Al-content AlGaN often results in a high density of threading dislocations and surface hexagonal hillocks, which degrade the performance and reliability of AlGaN-based UVC light emitting diodes (LEDs). In this study, the degradation mechanism and impurity/defect behavior of UVC LEDs in relation to the hexagonal hillocks have been studied in detail. It was found that the early degradation of UVC LEDs is primarily caused by electron leakage. The prominent contribution of the hillock edges to the electron leakage is unambiguously evidenced by the transmission electron microscopy measurements, time-of-flight secondary ion mass spectrometry, and conductive atomic force microscopy. Dislocations bunching and segregation of impurities, including C, O, and Si, at the hillock edges are clearly observed, which facilitate the trap-assisted carrier tunneling in the multiple quantum wells and subsequent recombination in the p-AlGaN. This work sheds light on one possible degradation mechanism of AlGaN-based UVC LEDs. [ABSTRACT FROM AUTHOR]

A crack-free AlN film with 4.5 μm thickness was grown on a 2-inch hole-type nano-patterned sapphire substrates (NPSSs) by hydride vapor phase epitaxy (HVPE). The coalescence, stress evolution, and dislocation annihilation mechanisms in the AlN layer have been investigated. The large voids located on the pattern region were caused by the undesirable parasitic crystallites grown on the sidewalls of the nano-pattern in the early growth stage. The coalescence of the c-plane AlN was hindered by these three-fold crystallites and the special triangle void appeared. The cross-sectional Raman line scan was used to characterize the change of stress with film thickness, which corresponds to the characteristics of different growth stages of AlN. Threading dislocations (TDs) mainly originate from the boundary between misaligned crystallites and the c-plane AlN and the coalescence of two adjacent c-plane AlN crystals, rather than the interface between sapphire and AlN. [ABSTRACT FROM AUTHOR]

The aim of this paper is to model the effects of threading dislocations on both gate and drain currents of AlGaN/GaN high electron mobility transistors (HEMTs). The fraction of filled traps increases with the threading dislocations, while the trapping effects cause a decrease in drain current and an increase in gate leakage current. To model the drain current drop, the two simplified RC subcircuits with diodes are proposed to capture the charge trapping/detrapping characteristics. The trap voltages Vg_trap and Vd_trap generated by RC networks are fed back into the model to capture the effects of traps on drain current. Considering acceptor-decorated dislocations, we present a novel Poole–Frenkel (PF) model to precisely describe the reverse leakage gate current, which plays a dominant role in the gate leakage current. The proposed model, which uses physical parameters only, is implemented in Verilog-A. It is in excellent agreement with the experimental data. [ABSTRACT FROM AUTHOR]

The major issues confronting the performance of deep-UV (DUV) laser diodes (LDs) are reviewed along with the different approaches aimed at performance improvement. The impact of threading dislocations on the laser threshold current, limitations on heavy n- and p-doping in Al-rich AlGaN alloys, unavoidable electron leakage into the p-layers of (0001) LD structures, implementation of tunnel junctions, and non-uniform hole injection into multiple quantum wells in the active region are discussed. Special attention is paid to the current status of n- and p-type doping and threading dislocation density reduction, both being the factors largely determining the performance of DUV-LDs. It is shown that most of the above problems originate from intrinsic properties of the wide-bandgap AlGaN semiconductors, which emphasizes their fundamental role in the limitation of deep-UV LD performance. Among various remedies, novel promising technological and design approaches, such as high-temperature face-to-face annealing and distributed polarization doping, are discussed. Whenever possible, we provided a comparison between the growth capabilities of MOVPE and MBE techniques to fabricate DUV-LD structures. [ABSTRACT FROM AUTHOR]

• Thermionic emission model interpret well the electrical behavior in Pt/n-GaN Schottky contacts. • Characterization of residual point defects in Pt/n-type GaN Schottky contacts by using Fourier transform deep level transient spectroscopy. • Characterization of dislocations and stacking faultsin Pt/n-type GaNSchottky contacts by using transmission electron microscope. • Native point defects and threading dislocations could be considered at the cause of barrier inhomogeneity phenomena in Pt/n-type GaN Schottky contacts. An ideal metal/GaN interface is not usually possible and the surface states are often present at such interface and therefore affect the Schottky barrier diode (SBD) performance. In this work the interface states in Pt/n-type GaN SBD were extracted using temperature dependent forward current–voltage (I - V - T) characteristics over a large temperature range (80–400 K). The energy profile distribution of the density of interface states N SS (E) and its dependence on the temperature were determined from the bias and temperature dependence of the measured effective barrier height Ф 0 b n (V , T) and ideality factor n (V , T). It is shown that the interface states density at room temperature decreases with increasing energy with respect to the conduction band. It is shown that the effective Schottky barrier height (SBH) and ideality factor are correlated to the density of interface states. This result suggests that interface states density contributes to barrier inhomogeneities in Pt/n-type GaN SBD. Fourier transform deep level transient spectroscopy (FT-DLTS) has been employed to extract qualitative information about the native defects present in as-grown n-type GaN. From FT-DLTS, two prominent native defects D 2 and D 3 were observed in GaN. The defect D 2 located at E C - 0.56 eV could be associated with impurity at Ga site. The defect D 3 located at E C - 0.26 eV has been assigned to nitrogen-related energy level. These native defects are interpreted as responsible of the existence of interface states and then to the barrier inhomogeneities at Pt/n-type GaN contacts. Furthermore, other possible origins of the interface states at Pt/n-type GaN interface are discussed in terms of the threading dislocations inside the GaN templates that reach the surface and other possible irregularities at this interface. [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]

Heteroepitaxial growth of high Al-content AlGaN often results in a high density of threading dislocations and surface hexagonal hillocks, which degrade the performance and reliability of AlGaN-based UVC light emitting diodes (LEDs). In this study, the degradation mechanism and impurity/defect behavior of UVC LEDs in relation to the hexagonal hillocks have been studied in detail. It was found that the early degradation of UVC LEDs is primarily caused by electron leakage. The prominent contribution of the hillock edges to the electron leakage is unambiguously evidenced by the transmission electron microscopy measurements, time-of-flight secondary ion mass spectrometry, and conductive atomic force microscopy. Dislocations bunching and segregation of impurities, including C, O, and Si, at the hillock edges are clearly observed, which facilitate the trap-assisted carrier tunneling in the multiple quantum wells and subsequent recombination in the p-AlGaN. This work sheds light on one possible degradation mechanism of AlGaN-based UVC LEDs.

• Preferential etching at TD sites takes place in the porosification process of Ge-on-Si and is independent of the doping type and concentration. • For the morphology of penetrating pores, the porous Ge was in a dense columnar shape when the holes were supplied adequately. When the hole concentration is limited, dendritic pore shape was obtained, for example, in n -type Ge-on-Si with a doping concentration of 5E18 cm−3. • The penetrating pores at the TDs follow the path of the threading dislocation line and form a conical shape of the etched region. Since the TDs thread from the Ge/Si interface to the Ge surface, the etching along dislocations would ultimately penetrate the entire epitaxial Ge layer. • The origins of the preferential etching at TDs have been discussed to be lattice distortion in structure and negative charged in dislocation cores. Epitaxial Ge-on-Si possesses a high density of threading dislocations (TDs) due to the lattice mismatch and difference in thermal expansion coefficient. By employing the lattice distortion at the TDs, we demonstrate that penetrating pores along TDs can be formed in both p - and n -type heteroepitaxial Ge layers through a preferential etching. It has been found that the preferential etching at TD sites takes place in the porosification process of Ge-on-Si samples and is independent of the doping type and concentration. The penetrating pores follow the path of the TD lines and can penetrate the entire Ge layer of 1.3 μm to further porosificate the Si substrate. The effects of anodic current density and total etching duration have been thoroughly investigated on forming penetrating pores at TD sites. The dissolution mechanism in the porosification process has been revealed by dissolution valence calculation and recorded potential curves. Our findings shed light on Ge perforation in both p - and n -type Ge-on-Si and show great potential in Si-based integrated photonics and microelectronics. [ABSTRACT FROM AUTHOR]

The aim of this paper is to model the effects of threading dislocations on both gate and drain currents of AlGaN/GaN high electron mobility transistors (HEMTs). The fraction of filled traps increases with the threading dislocations, while the trapping effects cause a decrease in drain current and an increase in gate leakage current. To model the drain current drop, the two simplified RC subcircuits with diodes are proposed to capture the charge trapping/detrapping characteristics. The trap voltages Vg_trap and Vd_trap generated by RC networks are fed back into the model to capture the effects of traps on drain current. Considering acceptor-decorated dislocations, we present a novel Poole–Frenkel (PF) model to precisely describe the reverse leakage gate current, which plays a dominant role in the gate leakage current. The proposed model, which uses physical parameters only, is implemented in Verilog-A. It is in excellent agreement with the experimental data.

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]

The major issues confronting the performance of deep-UV (DUV) laser diodes (LDs) are reviewed along with the different approaches aimed at performance improvement. The impact of threading dislocations on the laser threshold current, limitations on heavy n- and p-doping in Al-rich AlGaN alloys, unavoidable electron leakage into the p-layers of (0001) LD structures, implementation of tunnel junctions, and non-uniform hole injection into multiple quantum wells in the active region are discussed. Special attention is paid to the current status of n- and p-type doping and threading dislocation density reduction, both being the factors largely determining the performance of DUV-LDs. It is shown that most of the above problems originate from intrinsic properties of the wide-bandgap AlGaN semiconductors, which emphasizes their fundamental role in the limitation of deep-UV LD performance. Among various remedies, novel promising technological and design approaches, such as high-temperature face-to-face annealing and distributed polarization doping, are discussed. Whenever possible, we provided a comparison between the growth capabilities of MOVPE and MBE techniques to fabricate DUV-LD structures.

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]

The kinematic and isotropic strain hardening was investigated in columnar-grained copper with preferentially oriented nanoscale twins deformed at two different strain rates of 5 × 10−5 and 5 × 10−3 s−1. A significant back stress is caused majorly by threading dislocation pile-up and accumulation at the grain boundaries and is strain rate independent. The isotropic hardening associated with an increment in the local effective stress stems from dislocation storage at twin boundaries, and a high strain rate is beneficial for enhancing isotropic strain hardening and tensile ductility. Impact statement Long-range back stress was detected to develop during plastic deformation of nanotwinned structures, majorly caused by pile-up and accumulation of threading dislocations at grain boundary regions.

We present the results of a transmission electron microscopy and X-ray diffractometry investigation of AlN/c-Al2O3 templates with GaN ultrathin insertions grown by plasma-assisted molecular beam epitaxy. It has been shown that AlN buffer layers with faceted surface morphology provide a greater threading dislocation density reduction than smooth layers. The filtering effect of GaN ultrathin insertions has been confirmed. [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]

In this paper we describe state-of-the-art approaches to the modeling of strain relaxation and dislocation dynamics in InGaAs/GaAs (001) heterostructures. Current approaches are all based on the extension of the original Dodson and Tsao plastic flow model to include compositional grading and multilayers, dislocation interactions, and differential thermal expansion. Important recent break-throughs have greatly enhanced the utility of these modeling approaches in four respects: i) pinning interactions are included in graded and multilayered structures, providing a better description of the limiting strain relaxation as well as the dislocation sidewall gettering; ii) a refined model for dislocation-dislocation interactions including zagging enables a more accurate physical description of compositionally-graded layers and step-graded layers; iii) inclusion of back-and-forth weaving of dislocations provides a better description of dislocation dynamics in structures containing strain reversals, such as strained-layer superlattices or overshoot graded layers; and iv) the compositional dependence of the model kinetic parameters has been elucidated for the InGaAs material system, allowing more accurate modeling of heterostructures with wide variations in composition. We will describe these four key advances and illustrate their applications to heterostructures of practical interest. [ABSTRACT FROM AUTHOR]

Since the invention of dislocation sidewall gettering (DSG) in 2000 the technique has been applied extensively in infrared focal-plane arrays and flat-panel displays. However, development of DSG technology has been guided mostly by empirical trials due to the lack of detailed physical models. Here we demonstrate the application of a dislocation dynamics model to evaluate DSG approaches in both ZnSySe1-y/GaAs (001) and InGaxAs1-x/GaAs (001) heterostructures. We find that the effectiveness of DSG is strongly dependent on composition in both material systems. [ABSTRACT FROM AUTHOR]

Strained-layer superlattices (SLSs) have been used to modify the threading dislocation behavior in metamorphic semiconductor device structures; in some cases they have even been used to block the propagation of threading dislocations and are referred to in these applications as "dislocation filters." However, such applications of SLSs have been impeded by the lack of detailed physical models. Here we present a "zagging and weaving" model for dislocation interactions in multilayers and strained-layer superlattices, and we demonstrate the use of this model to the threading dislocation dynamics in InGaAs/GaAs (001) structures containing SLSs. [ABSTRACT FROM AUTHOR]

Metamorphic semiconductor devices often utilize compositionally-graded buffer layers for the accommodation of the lattice mismatch with controlled threading dislocation density and residual strain. Linear or step-graded buffers have been used extensively in these applications, but there are indications that sublinear, superlinear, S-graded, or overshoot graded structures could offer advantages in the control of defect densities. In this work we compare linear, step-graded, and nonlinear grading approaches in terms of the resulting strain and dislocations density profiles using a state-of-the-art model for strain relaxation and dislocation dynamics. We find that sublinear grading results in lower surface dislocation densities than either linear or superlinear grading approaches. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Si (001) substrates with a kind of special sub-nano streaky surface are etched at atomic resolution. • The sub-nano streaky surface is prepared by utilizing a special pattern of H 2 SO 4 residue and then etching with HF. • The Si (001) substrates with sub-nano streaky surface are proved to be very advantageous for III/V growth. • The generation of antiphase-boundaries at the very beginning of the GaAs growth is completely prevented. • This substrate can enhance the overall crystalline quality, for example, achieving low threading dislocation density. The Si (001) substrates with a kind of special sub-nano streaky surface were prepared and applied to high-quality growth of GaAs heteroepitaxial-layers. The morphology of each of them features a series of parallel but randomly intermittent streaks along a common fixed direction and individually with their own saw-tooth cross-sections. The lateral interval between any two adjacent streaks is bound to be in sub-nano scale and both the two side-facets of every cross-section sawtooth are {111} planes. It has been found that the direct growth of GaAs epilayers on this kind of substrates, especially on exactly (001) oriented ones, can not only completely prevent the antiphase boundaries (APBs) generation, but also significantly reduce the threading dislocation density (TDD). This advancement could be regarded as a nearly perfect solution to APBs elimination and, moreover, provides better basis for further TDD reduction in the preparation of III-V/Si epilayers and for relevant device fabrications. [ABSTRACT FROM AUTHOR]

We conducted a modeling study of the threading dislocation behavior in chirped and unchirped InGaAs/GaAs (001) strained-layer superlattices (SLSs) using a Dodson & Tsao / Kujofsa & Ayers (DTKA) type plastic flow model. Four types of SLSs were investigated: type I was chirped using compositional modulation, type II was chirped using layer thickness modulation, type III was unchirped with alternating layers of InGaAs and GaAs, and type IV was unchirped with alternating layers of InGaAs having two different compositions. Generally the surface and average values of the dislocation density decreased with increasing total thickness. The dependence on top indium composition was more complex, due to dislocation compensation and multiplication effects, but for type II and IV superlattices, the average and surface threading dislocation densities increased in nearly monotonic fashion with top indium composition. Based on these results, the compositionally-modulated chirped (type I) and InGaAs/GaAs unchirped (type III) superlattices appear to be best suited as buffer layers for metamorphic devices, while the chirped superlattices with layer thickness modulation (type II) and InGaAs/InGaAs unchirped (type IV) superlattices appear to be poorly suited for use as buffer layers for devices containing high indium content. [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]

Abstract High-efficiency semiconductor lasers and light-emitting diodes operating in the 3–5 μm mid-infrared (mid-IR) spectral range are currently of great demand for a wide variety of applications, in particular, gas sensing, noninvasive medical tests, IR spectroscopy etc. III-V compounds with a lattice constant of about 6.1 Å are traditionally used for this spectral range. The attractive idea to fabricate such emitters on GaAs substrates by using In(Ga,Al)As compounds is restricted by either the minimum operating wavelength of ∼8 μm in case of pseudomorphic AlGaAs-based quantum cascade lasers or requires utilization of thick metamorphic In x Al 1 -x As buffer layers (MBLs) playing a key role in reducing the density of threading dislocations (TDs) in an active region, which otherwise result in a strong decay of the quantum efficiency of such mid-IR emitters. In this review we present the results of careful investigations of employing the convex-graded In x Al 1 -x As MBLs for fabrication by molecular beam epitaxy on GaAs (001) substrates of In(Ga,Al)As heterostructures with a combined type-II/type-I InSb/InAs/InGaAs quantum well (QW) for efficient mid-IR emitters (3–3.6 μm). The issues of strain relaxation, elastic stress balance, efficiency of radiative and non-radiative recombination at T = 10–300 K are discussed in relation to molecular beam epitaxy (MBE) growth conditions and designs of the structures. A wide complex of techniques including in-situ reflection high-energy electron diffraction, atomic force microscopy (AFM), scanning and transmission electron microscopies, X-ray diffractometry, reciprocal space mapping, selective area electron diffraction, as well as photoluminescence (PL) and Fourier-transformed infrared spectroscopy was used to study in detail structural and optical properties of the metamorphic QW structures. Optimization of the growth conditions (the substrate temperature, the As 4 /III ratio) and elastic strain profiles governed by variation of an inverse step in the In content profile between the MBL and the InAlAs virtual substrate results in decrease in the TD density (down to 3 × 107 cm−2), increase of the thickness of the low-TD-density near-surface MBL region to 250–300 nm, the extremely low surface roughness with the RMS value of 1.6–2.4 nm, measured by AFM, as well as rather high 3.5 μm-PL intensity at temperatures up to 300 K in such structures. The obtained results indicate that the metamorphic InSb/In(Ga,Al)As QW heterostructures of proper design, grown under the optimum MBE conditions, are very promising for fabricating the efficient mid-IR emitters on a GaAs platform. [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]

Metamorphic realization of semiconductor devices has become increasingly important due to the great freedom it affords in layer compositions and thicknesses. However, metamorphic growth is often accompanied by the introduction of high densities of threading dislocation defects. This behavior may be understood by using an annihilation and coalescence model for the threading dislocation behavior which is based on the dislocation interaction length Lint. For its application we considered only glide of dislocations, so the interaction length was assumed to be equal to the length of misfit dislocation segments LMD. The length of misfit segments was determined approximately by the Matthews, Mader, and Light model [J. Appl. Phys., 41, 3800 (1970)] for lattice relaxation, and was assumed to be independent of the distance from the interface. Within this framework we have applied the annihilation and coalescence model to chirped semiconductor superlattices to evaluate these superlattices as strainrelaxed buffers for metamorphic devices. In this work we have studied two basic types of InGaAs/GaAs chirped superlattice buffers: type I superlattices are compositionally modulated while type II superlattices are thickness modulated. [ABSTRACT FROM AUTHOR]

Metamorphic semiconductor devices such as high electron mobility transistors (HEMTs), light-emitting diodes (LEDs), laser diodes, and solar cells are grown on mismatched substrates and typically exhibit a high degree of lattice relaxation. In order to minimize the incorporation of threading defects it is common to use a linearly-graded buffer layer to accommodate the mismatch between the substrate and device layers. However, some work has suggested that buffer layers with non-linear grading could offer superior performance in terms of limiting the surface density of threading defects. In this work, we have compared S-graded buffer layers with different orders and thicknesses. To do so we calculated the expected surface threading dislocation density for each buffer design assuming a GaAs (001) substrate. The threading dislocation densities were calculated using the LMD model, in which the coefficient for second-order annihilation and coalescence reactions between threading dislocations is considered to be equal to the length of misfit dislocations. [ABSTRACT FROM AUTHOR]

Several simple models have been developed for the threading dislocation behavior in heteroepitaxial semiconductor materials. Tachikawa and Yamaguchi [Appl. Phys. Lett., 56, 484 (1990)] and Romanov et al. [Appl. Phys. Lett., 69, 3342 (1996)] described models for the annihilation and coalescence of threading dislocations in uniform-composition layers, and Kujofsa et al. [J. Electron. Mater., 41, 2993 (2013)] extended the annihilation and coalescence model to compositionally-graded and multilayered structures by including the misfit dislocation-threading dislocation interactions. However, an important limitation of these previous models is that they involve empirical parameters. The goal of this work is to develop a predictive model for annihilation and coalescence of threading dislocations which is based on the dislocation interaction length Lint. In the first case if only in-plane glide is considered the interaction length is equal to the length of misfit dislocation segments while in the second case glide and climb are considered and the interaction length is a function of the distance from the interface, the length of misfit dislocations, and the density of the misfit dislocations. In either case the interaction length may be calculated using a model for dislocation flow. Knowledge of the dislocation interaction length allows predictive calculations of the threading dislocation densities in metamorphic device structures and is of great practical importance. Here we demonstrate the latter model based on glide and climb. Future work should compare the two models to determine which is more relevant to typical device heterostructures. [ABSTRACT FROM AUTHOR]

The kinematic and isotropic strain hardening was investigated in columnar-grained copper with preferentially oriented nanoscale twins deformed at two different strain rates of 5 × 10−5 and 5 × 10−3 s−1. A significant back stress is caused majorly by threading dislocation pile-up and accumulation at the grain boundaries and is strain rate independent. The isotropic hardening associated with an increment in the local effective stress stems from dislocation storage at twin boundaries, and a high strain rate is beneficial for enhancing isotropic strain hardening and tensile ductility. Impact statement Long-range back stress was detected to develop during plastic deformation of nanotwinned structures, majorly caused by pile-up and accumulation of threading dislocations at grain boundary regions. [ABSTRACT FROM AUTHOR]

In this paper, the advantages of GaN high electron mobility transistors (HEMTs) grown on native GaN over GaN/Si or GaN/sapphire substrates are investigated and correlated with epitaxial material quality. Transmission electron microscopy plan-view and cross-sectional analyses of GaN/GaN reveal dislocation densities below ${1} \times {10}^{{6}}$ cm−2, which is at least three orders of magnitude lower than that of GaN/Si or GaN/sapphire. In the case of GaN/Si, the dislocations not only originate from the substrate/nucleation layer interface, but also the strain relief and isolation buffer stacks are main contributors to the dislocation density. GaN/GaN HEMTs show superior electrical and thermal performance and feature three orders of magnitude lower OFF-state leakage. The current collapse (also referred to as current dispersion or $R_{ \mathrm{\scriptscriptstyle ON}}$ -increase) after stress bias is less than 15% compared with 50% in the case of GaN/Si. A 2% drop of the ON-state current due to self-heating in dc operation when compared with 13% and 16% for GaN/Si and GaN/sapphire, respectively. The GaN/Si thermal performance becomes comparable to that of GaN/GaN only after substrate removal. Therefore, GaN/GaN provides high ON-state current, low OFF-state leakage current, minimal current collapse, and enhanced thermal power dissipation capability at the same time, which can directly be correlated with the absence of high dislocation density. [ABSTRACT FROM AUTHOR]

In order to evaluate various buffer layers for metamorphic devices, threading dislocation densities have been calculated for uniform composition InxGa1−xAs device layers deposited on GaAs (001) substrates with an intermediate graded buffer layer using the LMD model, where LMD is the average length of misfit dislocations. On this basis, we compare the relative effectiveness of buffer layers with linear, exponential, and S-graded compositional profiles. In the case of a 2 μm thick buffer layer linear grading results in higher threading dislocation densities in the device layer compared to either exponential or S-grading. When exponential grading is used, lower threading dislocation densities are obtained with a smaller length constant. In the S-graded case, lower threading dislocation densities result when a smaller standard deviation parameter is used. As the buffer layer thickness is decreased from 2 μm to 0.1 μm all of the above effects are diminished, and the absolute threading dislocation densities increase. [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]

In this work we investigated the dislocation-dependent behavior of Pendellösung fringes from two types of semiconductor heterostructures: a uniform-composition InGaAs epitaxial layer grown on a GaAs (001) substrate with an intermediate step-graded InGaAs buffer, and an InGaAs/InAlAs high electron mobility transistor grown on an InP (001) substrate. Dynamical x-ray diffraction simulations were carried out in the 004, 115,135, and 117 geometry, assuming Cu kα incident radiation, for both structures. The dislocation density strongly affects the intensities and widths of Pendellösung fringes, and we have established quantitative relationships which will allow characterization of the dislocation density. [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]

Micro-nano ultraviolet light sources have recently attracted great attention due to their promising applications in future quantum display, photoelectric detection sensors, biomedical devices, and so on. Design of ultraviolet light sources with smaller size, stronger emission intensity, and higher integration, are the key aspects for the development of high-performance micro-nano ultraviolet devices. Here, we demonstrate that unidirectional threading dislocation arrays in an AlN thin film can emit ultraviolet light with wavelength of ∼ 317 nm. The density of AlN dislocations is ∼ 4 × 1010 cm−2, and the light emission intensity of AlN dislocations is comparable to the intrinsic emission of the AlN thin film. By combining aberration-corrected transmission electron microscopy, atomic-resolution valence electron energy-loss spectroscopy, and first-principles calculations, the atomic and electronic structures and the band gaps of the AlN threading dislocations are determined. It is found that the AlN threading dislocations are comprised of edge, screw, and mixed dislocations. All the AlN dislocations exhibit smaller band gaps compared to the AlN bulk due to the increase of the Al-N bond length at the dislocation cores. The dangling bonds of Al and N at the edge dislocations, Al-Al and N N bonds at the screw dislocations cause the defect states in the band gaps. This study not only has clarified the atomic origin of dislocation nano-optics, but also will encourage the development of microelectronics and optoelectronic devices based on dislocation ultraviolet light emission. [Display omitted] [ABSTRACT FROM AUTHOR]

A simple model that establishes a quantitative measure for the positional correlation degree of threading dislocations (TDs) in heteroepitaxial layers is proposed. Accordingly, analyzing the linewidth of the Gaussian fit that follows the experimental rocking curve (RC), we obtained the correlation degree of screw and edge TDs in GaN epitaxial layers grown on sapphire substrate. Calculating the numerical integral using both the standard Wilkens correlation parameter, M , and the new one, S , and comparing the numerical results with the experimental diffraction patterns for three samples of GaN epitaxial films with different thicknesses, we demonstrate that the newly determined correlation parameter is correct. [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]

In this letter, we have examined the impact of trench dimensions on the breakdown voltage and ON-resistance of trench MOSFETs fabricated on sapphire and bulk GaN substrates. Contrary to simulation studies, the breakdown voltage decreased with an increase in trench dimensions in devices fabricated on sapphire substrates. However, such breakdown voltage dependence with trench dimensions was not observed in devices fabricated on bulk GaN substrates of the same area. The observed trend on GaN on sapphire devices was associated with the equivalently reduced number of dislocations per device area. These results give an insight into how dislocations could affect breakdown voltage in power MOSFETs. [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]

In this paper, Si-doped GaN template layer and nitride-based multiple quantum well (MQW) light-emitting diodes (LEDs) with conventional GaN buffer layer and GaN buffer layer using SiN treatment were elaborated by metalorganic vapor phase epitaxy (MOVPE). On both kinds of structures, five InGaN/GaN quantum wells were deposited simultaneously in identical growth conditions. GaN template layer defects that influence on the growth of InGaN/GaN MQW LEDs were systematically studied by means of scanning electron microscopy, high-resolution x-ray diffraction, temperature-dependant photoluminescence measurement, and electroluminescence. It is shown that optical properties of InGaN/GaN MQWs depend on the defect density of elaborated templates. Thereafter, we report an enhancement of the emission of blue MQW LEDs using SiN treatment, compared to the MQW LED emissions deposited on a conventional GaN buffer layer. [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]

An investigation of the threading dislocations (TDs) density in two high quality GaN epitaxial layers grown on sapphire (Al 2 O 3 ) substrate, with the thickness of 300 and 1000 nm, respectively, is presented in this paper. In the case of GaN 300 sample, taking into account that the finite size effect exerts an increased influence, further advanced methods are necessary to find the correct results besides the standard analysis of the Full Width at Half Maximum (FWHM) of the X-ray rocking curves peaks as in the case of the thicker sample, GaN 1000. Thus, we explored the tails of the rocking curves using a universal power law fit and subsequently, we used modified version of the Williamson-Hall plots. Analysis of the XRD profiles allowed us to avoid the overestimation of the threading dislocations density determined by the influence of the correlation between dislocations. Moreover, we successfully separate the contribution of the strain and size broadening based on the analysis of refined Williamson Hall plots and demonstrate the nearly uniform dislocation density depth distribution of the GaN studied films, with no supplementary nucleation or annihilation centers are present inside the epitaxial film using, both grazing incidence and grazing exit configurations of the asymmetric geometry. [ABSTRACT FROM AUTHOR]

Linear piezoelectric formulations were employed to analytically evaluate the electroelastic fields generated by a single threading edge/screw dislocation in piezoelectric gallium nitride (GaN) thin film. All possible growth orientations, namely c -plane (polar), a - and m -planes (non-polar), and ( 11 2 ¯ 2 ) -plane (semi-polar) of GaN layers were considered for the analysis. Single piezoelectric threading edge and screw dislocations were also modeled by a commercial finite element analysis code, ABAQUS 6.14. The edge dislocation was modeled by invoking one-dimensional thermal strain analogy to effectively introduce an extra plane of atoms. The screw dislocation was modeled by creating a slip in opposite surfaces by applying opposite displacements of magnitude equal to half the Burgers vector parallel to the direction of the dislocation line. We also evaluated the Peach-Kohler force acting on a piezoelectric dislocation as well as the material force calculated by the J -integral. The effects of piezoelectricity and the line charge on electroelastic fields induced by a single dislocation were investigated for various growth orientations. We also evaluated the role of spontaneous polarization along c -direction in the presence of electroelastic fields generated by the dislocation. These results can be utilized in studying the influence of piezoelectric strains and electrical fields on the optoelectronic performance of GaN-based devices in the presence of dislocations. They can also be helpful in understanding the mechanics of misfit dislocations that form between the substrate and the film. [ABSTRACT FROM AUTHOR]

The threading dislocations in GaN provide diffusion routes for impurity incorporation, which substantially influences GaN based optoelectronic devices. Here, we investigated the characteristics of the impurity incorporation at threading dislocations by HCl vapor phase etching and cathodoluminescence (CL) measurements. The distinctive etch pits induced by HCl vapor phase etching correspond definitely to different types of dislocations, and the etching process causes simultaneously H incorporation at a high temperature. CL spectra of the etch pits were analyzed, and the observed difference in the redshift of near band emission peak indicates that mix dislocations are more favorable for impurity incorporations than that of edge dislocations. The understanding on the impurity incorporation behavior at threading dislocations helps to obtain high quality GaN nanostructures. [ABSTRACT FROM AUTHOR]