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To suppress wafer bowing and crack generation of GaN on Si substrates, we investigated the effects of the Al content and thickness of the AlGaN interlayer on the compressive strain in the overlying GaN layer theoretically and experimentally. In the simulation, AlGaN relaxes gradually over the critical thickness. Therefore, the relaxation ratio of AlGaN at the top surface can be defined as a function of Al content and thickness. Too high Al content or too thick AlGaN interlayer induced too large initial strain in the upper GaN layer, which caused rapid and succeeding gradual relaxation, i.e., decrease of strain, of the GaN layer during growth because of generation of threading dislocations. Conversely, low Al content or thin AlGaN interlayer could induce constant but only small strain in the GaN layer. Therefore, the ideal relaxation ratio of the AlGaN surface exists to apply the maximal constant compressive strain in the GaN layer. The relaxation ratios of AlGaN interlayers determined in experiments were much smaller than those calculated in the simulation. Although the measured compressive strain in the GaN layer was smaller than expected, its decrease rate was small when grown on AlGaN interlayers with an almost ideal relaxation ratio.

High quality In0.30Ga0.70As layers on GaAs substrates were obtained using compositional undulating step-graded Ga1-xInxP (x = 0.48–0.78) buffers grown by metal-organic chemical vapor deposition. The density of threading dislocation is about 4.0 × 106 cm−2 and the root-mean-square roughness is only 5.20 nm, which is much better than those grown on the conventional step-graded metamorphic buffer. On one hand, the reversed GaInP layers reduce the distribution imbalance of α dislocations between the (1 1 1) and (−1 −1 1) slip planes, which promote dislocation glide. On the other hand, the inserted tensile strained GaInP layers change the direction of dislocation glide and facilitate dislocation annihilations, which effectively confine the threading dislocations in the buffer. Overall, this work provides a promising way to obtain virtual substrates for the achievement of desired metamorphic devices.

To reduce the number of threading dislocations (TDs) in nonpolar a -plane GaN ( a -GaN) epi-layers grown on flat r -plane sapphire substrates ( r -FSS), we investigated the effects on the crystalline quality of the a -GaN epi-layers of high-density patterned r -plane sapphire substrates ( r -HPSS), the patterns of which were placed at intervals of several hundred nanometers. Two types of r -HPSS, the patterns of which had diameters and heights on the order of several hundred nanometers ( r -NHPSS) or several micrometers ( r -MHPSS), were prepared with conventional r -FSS. The effect of these r -HPSS on the a -GaN epi-layers was demonstrated by evaluating the surface morphology and the crystalline quality of the epi-layers. The surfaces of the a -GaN epi-layer grown on r -FSS and r -NHPSS were pit-free and mirror-like, whereas the surface of the a -GaN epi-layer grown on r -MHPSS was very rough due to the large, irregular GaN islands that grew on the patterns, mainly at the initial growth stage. The crystalline quality of the a -GaN epi-layer grown on r -NHPSS was better than that of the a -GaN epi-layer grown on r -FSS. We confirmed that there were fewer TDs in the a -GaN epi-layer grown on r -NHPSS than there were in the a -GaN epi-layer grown on r -FSS. The TDs propagating to the surface in a -GaN epi-layer grown on r -NHPSS were mainly generated on the flat sapphire regions between the patterns. Interestingly, it was also found that the TDs that propagated to the surface concentrated with a periodic pitch along the c -axis direction. The TD densities of a -GaN epi-layers grown on r -FSS and r -NHPSS were estimated to be approximately 5.0 × 10 10 and 1.5 × 10 9 cm −2 , respectively. This knowledge will contribute to the further development of a -GaN epi-layers for high-performance devices.

Threading dislocations in a heteroepitaxial α-Ga2O3 film was visualized as etch pits on the surface. We found that etch pits were formed on a c-plane α-Ga2O3 epilayer by HCl gas etching. The epilayer was prepared by using epitaxial lateral overgrowth technique with a stripe mask pattern. The etch pit density was very high in the window region, and much lower in the laterally grown area on the mask. A line of etch pits was observed at a coalesced boundary. Thus, the etch pit density had a clear correlation with the dislocation density. The correspondence between the etch pits and dislocations was confirmed by cross-sectional bright- and dark-field transmission electron microscopy (TEM). This gas-etching technique can clarify the distribution of dislocations in a wide area, which cannot be explored effectively by TEM.

In this work GaN films are grown on 4H-SiC substrates with different surface terrace step width and the influence of the step width on the crystal quality of GaN is studied using X-ray diffraction (XRD) method. The results prove that the different surface terrace step width has a big impact on the (0 0 2) and (1 0 2) full width at half maximum (FWHM) of GaN films. It is mainly because the nucleation and coalescence mechanism of AlN is closely related with the surface step width, resulting in different densities of threading dislocations in the subsequent grown GaN films.

High-resistance GaN with low dislocation density adopting growth mode modification has been investigated by metalorganic chemical vapor deposition. The sheet resistance of the order of 1016 Ω/sq has been achieved at room temperature by diminishing the oxygen impurity level close to the substrate with an AlN blocking layer. Attributed to this method which offers more freedom to tailor the growth mode, a three-dimensional (3D) growth process is introduced by adjusting the growth pressure and temperature at the initial stage of the GaN epitaxy to improve the crystalline quality. The large 3D GaN grains formed during this period roughen the surface, and the following coalescence of the GaN grains causes threading dislocations bending, which finally remarkably reduces the dislocation density.

A TEM study of defect structure of GaN films grown by chloride vapor-phase epitaxy (HVPE) on GaN/Al 2 O 3 substrates was performed. The substrates were fabricated by metal-organic chemical vapor deposition overgrowth of templates with buried column pattern. The results of TEM study showed that the character of the defect structure of HVPE-grown films was determined by the configuration of the column pattern in the substrate. By choosing the proper pattern, the reduction in the density of threading dislocations in the films by two orders of magnitude (in respect to the substrate material), down to the value of 10 7 cm −2 , was achieved.

In-situ etching of GaAs with CBr 4 in metalorganic vapor phase epitaxy has been investigated at different temperatures using in-situ reflectivity to measure the etch rates. Deep (150 nm) etching of epitaxially-grown GaAs leads to the development of etch pits on the surface, corresponding to the emerging points of threading dislocations. Addition of trimethylgallium (TMGa) leads to a linear superposition of growth and etching. Trimethylaluminium (TMAl) added in moderate quantity enhances the etch rate and inhibits the development of etch pits. A model description for the enhanced etch rate is presented.

SiGe films were grown on a chemical vapor deposition (CVD)-grown Si0.88Ge0.12/Si (0 0 1) graded film with different growth solution compositions using a temperature interval of 950-940 °C by liquid phase epitaxy (LPE). The LPE films grown on the CVD-grown SiGe/Si (0 0 1) graded film are ≥86% relaxed, much more relaxed than those on bare Si (Wang and Quitoriano, 2019) since the existing threading dislocations in the CVD-grown SiGe/Si (0 0 1) graded film glide to create misfit dislocations without needing to nucleate new ones. The threading dislocation density of the LPE films is slightly lower than that of the CVD-grown SiGe films and on the same order of magnitude, ~106 cm−2. Since the CVD-grown SiGe/Si (0 0 1) graded film was annealed for 4 h before the LPE growth occurred, the properties of the CVD-grown SiGe/Si (0 0 1) graded film were studied and we found that the CVD-grown SiGe/Si (0 0 1) graded film have SiGe islands appear all over the surface aligned along the 〈1 1 0〉 crosshatch morphology and become more relaxed after annealing.

We report reducing the density of threading dislocations (TDs) in stacking-fault-free semipolar (20 2 ¯ 1 ) GaN grown on sapphire by inserting an AlGaN/GaN superlattice (SL). We have studied the influence of AlGaN/GaN SL on the reduction of TDs and found that the density of TDs decreases by more than a factor of three with increasing the number of AlGaN/GaN SL pairs up to 10. Furthermore, blue light emitting diodes (LEDs) have been grown on semipolar (20 2 ¯ 1 ) GaN/sapphire templates with inserted 10 pairs of AlGaN/GaN SL showing doubled light output power in comparison with the LEDs grown without AlGaN/GaN SL.

Deflection of threading dislocations in patterned 4H–SiC epitaxial growth is investigated by applying multiple dry etching to create stair-like patterns growing toward 1 1 ¯ 00 > on 11 2 ¯ 0 > off-cut Si-face and C-face substrates. Forced deflection of most threading dislocations in the substrate is accomplished in the patterned C-face epitaxial growth; although no remarkable deflection of threading dislocations takes place in the patterned Si-face growth. The morphology of the patterned steps and behavior of threading and deflected dislocations are examined by optical microscopy and synchrotron X-ray topography, respectively. The interactions between the patterned steps and dislocations as well as the dependency of the deflection ratios of threading dislocations on the morphology of patterned steps are discussed.

The arrays of edge threading dislocations (TD) have been observed in highly dislocated GaN film grown on Al 2 O 3 (0001) substrate. There are three kinds of arrays including straight-row, partial-circle and full-circle arrays. A theoretical model derived from the thermodynamics of grains evolution during the GaN recrystallization was used to explain the appearance of these arrays and the statistical distribution of edge TDs. Both the theoretical and experimental results show a Weibull distribution of edge TDs. It is concluded that in crystalline GaN epitaxial films, the edge TD arrays originate from grain coalescence after the recrystallization.

Epitaxial films of AlN were grown on a sapphire substrate with a miscut of 0.38°±0.02° towards the m-plane by metalorganic vapour phase epitaxy. A low temperature nucleation layer was used to overcome growth instabilities and to suppress the formation of inversion domains. This was followed by high temperature growth at 1250 °C. This two-step process, gives an acceptable material quality, (0002 FWHM=398±10′′ and 10–11 FWHM=940±23′′), but resulted in a top surface dominated by large steps, with average heights of 6.0±0.5 nm. Atomic force microscopy analysis of step termination sites shows a staircase of single and double atomic steps, showing large steps are formed by the bunching of single steps, perhaps pinned by threading dislocations. To achieve a smooth top surface, 100 nm of the high temperature AlN is followed by growth at 1110 °C. This three step process largely eliminates the large steps resulting in a layer that has a smooth surface morphology and lower defect density (0002 FWHM=351±9′′ and 10–11 FWHM=761±19′′).

In this article, we analyze the behavior of threading dislocations in GaN layers re-grown on hexagonally patterned mask-less GaN. The growth mode of the material with patterned hexagonal morphology changes with the diameter and the periodicity of the hexagonal patterns. The growth mode directly affects the shape of the voids that are formed in this kind of lateral epitaxy. Transmission electron microscopy has been used to study threading dislocations in GaN layers with voids having different sizes and sidewall angles. The results show that a significant number of threading dislocations near the tapered void's surface undergo a 90° reorientation in their propagation trajectory whereas almost no dislocations bend in the case of smaller voids having more vertical sidewalls. Different types of dislocations in the vicinity of the voids have also been identified using the invisibility g·b criteria. The full width at half maximum values for XRD ω -scan recorded in (002) reflection drop from 256″ to 181″ as the void sidewall inclination changes from 85° to 60°. A similar dropping trend in the full width at half maximum values for asymmetric diffraction reflections has also been observed.

V-shaped pits (V-defects) were observed in semipolar (1122)-oriented InGaN/GaN layers grown by plasma-assisted molecular beam epitaxy (PA-MBE). The pit morphology was that of inverted rhombic or trigonal pyramids aligned along the in-plane [1100] direction. Pit facet orientations were identified. The surface pits were found to be connected at their apex to mixed type a + c threading dislocations with large screw components. Such dislocations exhibited [1120] average line directions with zig-zag 〈1010〉 local lines, and they also induced V-defects at the InGaN/GaN interface.

Transmission electron microscopy (TEM) studies of defects in Al x Ga 1− x N layers with various Al mole fractions ( x =0.2, 0.4) and polarities were carried out. The samples were grown by ammonia molecular beam epitaxy on sapphire substrates and consisted of low-temperature AlN (LT-AlN) and high-temperature AlN (HT-AlN) buffer layers, a complex AlN/AlGaN superlattice (SL) and an Al x Ga 1− x N layer ( x =0.2, 0.4). It was observed that at the first growth stages a very high density of dislocations is introduced in both Al-polar and N-polar structures. Then, at the interface of the LT-AlN and HT-AlN layers half-loops are formed and the dislocation density considerably decreases in Al-polar structures, whereas in the N-polar structures such a behavior was not observed. The AlN/AlGaN superlattice efficiently promotes the bend and annihilation of threading dislocations and respectively the decrease of the dislocation density in the upper Al x Ga 1− x N layer with both polarities. The lattice relaxation of metal-polar Al 0.2 Ga 0.8 N was observed, while N-polar Al 0.2 Ga 0.8 N did not relax. The dislocation densities in the N-polar Al 0.2 Ga 0.8 N and Al 0.4 Ga 0.6 N layers were 5.5×10 9 cm −2 and 9×10 9 cm −2 , respectively, and in metal-polar Al 0.2 Ga 0.8 N and Al 0.4 Ga 0.6 N layers these were 1×10 10 cm −2 and 6×10 9 cm −2 , respectively. Moreover, from TEM images the presence of inversion domains (IDs) in N-polar structures has been observed. The widths of IDs varied from 10 to 30 nm. Some of the IDs widen during the growth of the AlN buffer layers. The IDs formed hills on the surface of the N-polar structures.

We study coalescence defects and their possible origins for Ge growth within parallel SiO 2 trenches created on (001) Si along [110] and [100] directions and (001) Ge substrates along [110]. Prior to coalescence, defects are not observed at the top of Ge, emerging from within trenches during lateral growth over the SiO 2 template. However, for Ge on Si growth, coalescence of Ge growing from adjacent trenches leads to twin defects and threading dislocations that originate from the top center and top corners of the SiO 2 walls, respectively. For Ge-on-Ge homoepitaxy, twins and threading dislocations are observed in Ge above the top center of the SiO 2 , but dislocations are not observed at the top corners of the SiO 2 walls. The twin defects are preferentially aligned along the same direction as channels patterned along [110] (twin density of 1.5×10 7 cm −2 ), but not for channels patterned along [100] (twin density of 2.5×10 7 cm −2 ). Finite element modeling is used to calculate the thermal stresses occurring in Ge and reveals that maximum thermal stress occurs near the top corners of the SiO 2 walls, where the threading dislocations (density of 7.2×10 7 cm −2 ) are experimentally observed in Ge grown on Si.

This paper demonstrates the use of Sidewall Lateral Epitaxial Overgrowth (S-LEO) on a -plane GaN thick films on r -plane sapphire by hydride vapor phase epitaxy (HVPE). Comprehensive study of the extended defect microstructure of the a -plane GaN films was carried out using cross-sectional and plan-view transmission electron microscopy (TEM). A very low density of primary threading dislocations and a heterogeneous microstructure can be found in the GaN films. In the window region and N-face wing region, the extended defects included type I 1 and type I 2 basal stacking faults (BSFs), as well as prismatic stacking faults (PSFs) on a -planes. The density of type I 1 BSFs was in the order of ∼2×10 5 cm −1 , type I 2 BSFs in the order of ∼10 4 cm −1 , and corresponding localized partial dislocation density less than 1.5×10 9 cm −2 . PSFs on a -planes were connected to two neighboring type I 1 BSFs with an estimated density of 3×10 2 cm −1 in the plan-view images. In the Ga-face overgrowth regions, the density of BSFs was lower than 10 4 cm −1 . However, inversion domains bounded by (1 1 0 2), (1 1 0 2), and (1 1 0 0) planes were found in the Ga-face wing regions. The nature of inversion domain boundaries (IDB) on m -planes can be explained by the Auserman-Gehamn model using high-angle annular dark-field TEM images.

The configurations and distributions of triangular pyramid etch pits on the (1 1 1)B face of CdZnTe revealed by Everson etch were studied using a scanning electron microscope (SEM), an optical microscope and a confocal laser scanning microscope (CLSM). Six types of triangular pyramid etch pits with different configurations were observed, one for the first time. These etch pits correspond to threading dislocations in the materials. By measuring the depths and orientations of the pit tips as well as the side lengths of the triangular pits on the surface, the orientations of the dislocations were determined. They are 〈2 1 1〉, 〈1 3 1〉, 〈1 1 1〉, 〈1 5 1〉, 〈0 3 1〉 and 〈1 1 0〉 for the six types of triangular pyramid etch pits. Among them, dislocations with 〈2 1 1〉, 〈1 1 1〉, 〈1 5 1〉 and 〈0 3 1〉 orientations have higher densities in CdZnTe materials. It was also found that the proportion of triangular pyramid etch pit to total etch pits is variable for different CdZnTe wafers and related to the stoichiometry of CdZnTe melt. These results show that Everson etch can reveal more information of CdZnTe materials than etch pit density (EPD).

KOH etching and high-resolution X-ray diffractometry (HRXRD) were used to study the evolution and structure of low-angle grain boundaries (LAGBs), which extended along 〈1 -1 0 0〉 in 6H–SiC bulk crystals grown by the sublimation method. It was found that LAGBs formed in the growth process consisted of an array of threading dislocations and took different configurations under different radial temperature gradients (RTGs). HRXRD results proved that the domain at one side of LAGBs formed under a low radial temperature gradient has only tilts around the c -axis with respect to the other domain at another side of LAGBs.

Cubic layered heterostructures are indispensable features of many electronic devices; however, the lattice mismatch tends to induce defects, e.g. dislocations. Glissile 60° misfit dislocations (MDs) generally form in the early stage of strain relaxation. During annealing, each relaxing 60° dislocation compensated-pair (60DCP) (with canceling screw and interface-perpendicular edge components) may coalesce into a 90° (pure edge) dislocation, which is a possible mechanism for the reduction of threading dislocations (TDs) through annealing. In this paper, we calculate the formation energies of periodic one-dimensional (1D) and two-dimensional (2D) arrays on the basis of linear elasticity. Each 1D 60DCP array always has lower energy than its homogeneous counterpart. The situation of each 2D array (containing two mutually orthogonal 1D arrays) depends on the period difference δ between the two individual 1D arrays and the film thickness. If δ =0, each 2D 60DCP array has higher energy than its homogeneous counterpart, whereas the 2D 60DCP array is energetically more favorable for a larger δ and/or a thicker film. The analysis suggests a semiconductor-processing strategy to obtain 90° dislocation-dominant arrays and to reduce TDs. Furthermore, based on the criterion of zero energy change by inserting the last dislocation to complete an array, we calculate the equilibrium array period for various configurations, implying possible strain over-relaxation (>100%-relaxed condition) for a sufficiently thick film.

The stress evolution of Si-doped AlxGa1−xN epilayers with x ranging from 0 to 0.62 was examined using an in situ wafer curvature measurement technique. Transmission electron microscopy was used to assess the effects of Si concentration and composition on defect microstructure. It was found that the density of edge-type threading dislocations (TDs) increased with increasing x, corresponding to the evolution of higher magnitudes of tensile stress, attributed to TD inclination. The results are discussed in the context of proposed inclination mechanisms that feature jog formation as the process leading to TD inclination.

A detailed study is presented on the influence of Mn-doping on densities of screw (c-type) and edge (a-type) threading dislocations (TDs) in Ga 1− x Mn x N grown by metal organic chemical vapor deposition (MOCVD) by using high-resolution X-ray diffraction (XRD). Three regions were present in Mn source rate dependence plots of density of c-TDs, and the mean twist angle corresponding to the density of a-TDs. In each region, Mn-doping exhibits different effects on the densities of a- and c-TDs, which is attributed to different dependences of the two types of TD on stresses. The results obtained from X-ray diffraction are consistent with those of atomic force microscope (AFM) measurements. It is further suggested that similar phenomena would occur when doping other elements into GaN grown by MOCVD.

The domain structures and dislocations in epitaxial thin films of La0.7Ca0.3MnO3 grown on SrTiO3 substrates by pulsed laser deposition were investigated using Bragg-contrast diffraction and high-resolution transmission electron microscopy. It revealed that the films contained the 1/2[100]o and 1/2[10-1]o types partial threading dislocations, the 90 degree - and 120 degree - types of twin- domain boundaries, and two types 1/2[010]o, 1/2[111]o, of antiphase boundaries, which are often observed in bulk materials. In addition, two types of superdislocations were detected; one consisted of two 1/2[111]o dislocations and a 1/2[111]o antiphase boundary, and the other was composed of two 1/2[010]o dislocations and a 1/2[010]o antiphase boundary. These superdislocations, domain boundaries, and their relationships were extensively explored., 19 pages, 6 figures

Fast-turnaround, accurate methods for the assessment of threading dislocation (TD) densities in GaN are an essential research tool. Here, we present an in situ surface treatment in which GaN is exposed to a SiH4 flux at 860 °C in the presence of NH3. Following a 240 s exposure to SiH4, pits associated with screw or mixed-type TD were found to have more than doubled in diameter, as measured by atomic force microscopy (AFM). These pits are associated with step-edge terminations. Additional small pits had appeared, not associated with step-edge terminations, which are believed to relate to edge-type TDs. The total density of pits on the treated surface corresponded to the total dislocation density measured by transmission electron microscopy. Pits related to edge-type TDs are often overlooked in AFM of untreated GaN. As the SiH4 treatment time is increased, the measured dislocation density initially increases, but after a 240 s treatment all the TDs may be observed. The pit width initially increases with treatment time, but then plateaus. The SiH4 treatment is effective in increasing dislocation pit size on both n- and p-type material, and has also been used on partially coalesced GaN layers.

The dislocation formation and propagation processes in physical vapor transport (PVT) grown 4H silicon carbide (4H–SiC) single crystals have been investigated using defect selective etching and transmission electron microscopy (TEM). It was found that while the growth initiation process generally increased the density of threading dislocations in the grown crystal, for certain areas of the crystal, threading dislocations were terminated at the growth initiation. Foreign polytype inclusions also introduced a high density of dislocations at the polytype boundary. In the polytype-transformed areas of the crystal, almost no medium size hexagonal etch pits due to threading screw dislocations were observed, indicating that the foreign polytype inclusions had ceased the propagation of threading screw dislocations. Based on these results, we argued the formation and propagation of the threading dislocations in PVT grown SiC crystals, and proposed the dislocation conversion process as a plausible cause of the density reduction of threading dislocations during the PVT growth of SiC single crystals.

We studied experimentally the crystallization of a low-temperature (LT)-GaN buffer layer and its effect on the subsequent crystalline quality of the GaN epitaxial layer. The degree of crystallization was sensitive to the thickness and the temperature ramp rate of the GaN buffer layer. When the LT-GaN buffer layer was more than 100 nm thick, there was relatively little crystallization of the buffer layer and subsequently poor crystalline quality of the GaN epitaxial layer. The optimum crystallization condition for the GaN buffer layer just prior to high-temperature growth was found when the single-crystal regions in the GaN buffer layer occupied a volume 40% as large as the randomly aligned matrix. We could reduce the threading dislocation density in the GaN epitaxial layer by inserting the LT-GaN buffer layers in periodically. To explain this result, we propose a mechanism by which the periodic layer reduces the density of threading dislocations.

Effects on structural characteristics of growth temperature and Si doping in GaN thin films grown on high temperature GaN was investigated. GaN/GaN homojunction structure was grown via metalorganic chemical vapour deposition at intermediate temperature (IT, 840°C) with various Si doping concentrations. V-shaped pits are observed on the surface of the undoped GaN grown at IT by atomic force microscopy analysis. Two beam images by transmission electron microscopy show that only screw- and mixed-type component of dislocations contributes to pit formation. Moderate Si doping reduces pit density but the over-doping of Si deteriorates the IT-GaN property by forming pits again. Not all pits are related with threading dislocations but some of them are observed in the dislocation free area of high Si-doped GaN.

Single-crystalline GaN/AlN layers have been grown on (1 1 1)Si substrates and subsequently used as the seeding layer for selective lateral overgrowth on a patterned Si 3 N 4 mask. GaN pyramids are formed during the lateral overgrowth. They are epitactically oriented with respect to the Si substrate with the orientation relationships [1 1 2 0] GaN ‖[ 1 1 0] Si and (0 0 0 1) GaN ‖(1 1 1) Si . The pyramids were characterized by transmission electron microscopy and were found to have a reduced defect density compared with continuous layers of GaN on Si and very few defects in the upper portion. The threading dislocations that originated from the GaN/AlN seeding layer eventually bend through 90° and emerge at the inclined surface. Many of the threading dislocations are actually half-loops which are self-terminating. The results of this study demonstrate that GaN selective lateral overgrowth can be performed on Si substrates and show that the same GaN crystalline quality can be produced on Si as on sapphire and SiC substrates.

We report on the structural properties of a series of thin GaN epilayers directly grown on on-axis 6H-SiC(0 0 0 1) by plasma-assisted MBE. X-ray measurements show that the crystalline perfection of the layers steadily improves with film thickness. In fact, the density of threading defects detected by transmission electron microscopy is found to decrease drastically with the distance away from the GaN/SiC interface, finally reaching a value of less than 5×10 9 cm −2 at a layer thickness of 0.5 μm. The formation mechanisms of the threading dislocations in the GaN films are discussed in consideration of the specific GaN/SiC interface structure.

Crack-free AlGaN with an Al content of 0.51 was successfully fabricated on selective-area-growth (SAG) GaN. To avoid the coalescence of the lateral overgrown GaN, the growth process of SAG-GaN was accurately controlled by in situ monitoring. Transmission electron microscopy (TEM) measurement demonstrated that the threading dislocations (TDs) disappeared from the SAG-GaN layer and appeared in the interface of SAG-GaN and AlGaN. Furthermore, the TDs in the AlGaN layer were mainly pure edge-type dislocations and the TD density of the AlGaN layer was about 1–3×10 8 cm −2 .

We estimated minority carrier diffusion length and lifetime of GaN and ZnSe using the electron-beam-induced current method. The minority carrier diffusion length of both p-type and n-type GaN is about 0.9 μm, which is comparable to that of ZnSe. The threading dislocation density in GaN on sapphire, however, is several orders larger than that in ZnSe on GaAs. Therefore, a comparison with ZnSe shows that threading dislocations in GaN on sapphire do not act as efficient trap centers for minority carriers.

Threading dislocations in the III-V heterostructure system are investigated based on the observation of dislocations in the In0.3Ga0.7As/GaAs superlattice with transmission electron microscope. To explain both the presence and orientation of threading dislocations in the epilayers an alloy effect on the dislocation lines in ternary III-V compounds is proposed, and, in addition, a pseudo-stable state for threading dislocations in binary compounds is recognized. (C) 1998 Elsevier Science B.V. All rights reserved.

Photoemission oscillations (PEO) are measured during the growth of InAs/AlSb/GaSb resonant tunneling diodes on (0 0 1) GaAs and (0 0 1) InAs substrates. PEO of the GaSb well are unresolved for growth on GaAs substrates but clearly observable for growth on InAs. AlSb barrier oscillations are observable on either substrate. The morphology of devices grown on GaAs is characterized by micron scale roughness whereas the devices grown on InAs are featureless on the same scale. Threading dislocations which terminate at the GaAs surface with a partial step are believed to influence the growth mode of GaSb but not AlSb due to the higher mobility of Ga in this system.

We have grown defect-free semiconductor-on-insulator (SOI) layers by liquid phase epitaxy. Defect-free Si layers grow laterally over SiO 2 by starting from seeding windows or ridge seeds on selectively oxide-masked (111) Si substrates. Growth is terminated when {111} facets at the sidewalls develop. The thin SOI layers are slightly bent in relation to the substrate and adhere firmly to the oxide film. The surface of defect-free SOI layers is formed by a perfect (111) facet, whereas monoatomic steps are found at the interfacial bottom of the layers. Although the Si layers are slightly bent, layers grown from different seeds may coalesce defect-free with seams of up to 150 μm in length. In SiGe layers on patterned Si substrates misfit and threading dislocations promote vertical growth of relaxed layers; SiGe layers grown laterally over oxide-covered Si substrates contain only few dislocations.

Misfit and threading dislocation morphologies and characteristics have been investigated in ∼ 1 μm thick GaAs films grown by molecular beam epitaxy on (110) Si with an off-angle of 6° toward the [001] direction using a transmission electron microscope. The short and segmented misfit dislocations of 60°- and 30°-type are mainly oriented to one ±[110] and two 〈112〉 directions, respectively, near the interface regions between GaAs and Si. On the other hand, most of the observed threading dislocations are 60°-type dislocations along the 〈110〉 direction and the [110] growth direction on inclined {111} planes together with screw-type threading dislocations running parallel to the [110] direction. It is considered that the 〈112〉- and ±[110]-oriented misfit dislocations change into the [110]- and 〈110〉-oriented threading dislocations, respectively, on either one of four {111} planes during growth. The effect of thermal annealing on the change of morphologies and density of these dislocations is also discussed.

The linearly-graded low-temperature buffer (LGLTB) approach developed by Harmand et al. [1] for growing materials with lattice parameters different from the substrate was extended to thick layers and minority carrier devices, using In x Ga 1- x As alloys with x =0.53 to 0.80 on InP. Structurally, the device layers were 90% to 100% relaxed with less than mid 10 5 cm -2 threading dislocations. Mobilities for 3 μm thick layers as well as modulation-doped structures of In 0.80 Ga 0.20 As were as high as 16,300 cm 2 /V·s at room temperature. p-n Homojunction diodes were nearly ideal and could be modeled with a diffusion-controlled leakeage current using minority carrier lifetimes of τ n = τ p =5×10 -9 s .

The morphology and distribution of dislocations in both single-layer and multiple-quantum-well Si 1− x Ge x /Si structures epitaxially grown by LPCVD between 700 and 750°C have been investigated by techniques of chemical etch, transmission electron microscopy and photoluminescence. A special morphology of initial-stage misfit dislocations and precipitate colonies formed along the misfit dislocations after annealing relaxation are presented and discussed. Dislocation-related photoluminescence has been distinguished and well correlated to the corresponding misfit and threading dislocations in the heterostructures. The combination of Schimmel etching and photoluminescence technique has allowed the experimental determination of the critical thickness of as-grown strained single layers grown at 750°C. A step-by-step etch in depth followed by taking photoluminescence spectra made possible the localization of the misfit dislocations in the multiple-quantum-well structures.

Accomodation of lattice mismatch is investigated for the case of large (ϵ>0.02) mismatch. In particular, the regime where the separation D between misfit dislocations is much less than the strained layer thickness h is considered here. The conventional Matthews-Blakeslee mechanism for creation of misfit dislocations is found to be inadequate for the case of large lattice relaxation owing to interactions amongst the misfit dislocations at the interface. According to St. Venant's principle, the stress fields of the dislocation network are screened beyond a distance D from the dislocation cores. This observation has several consequences, including large densities of threading dislocations and the “melting” of moderately relaxed heterointerfaces at conventional semiconductor growth temperatures. A number of experimental observations may be explained via these models.

Almost perfect multilayers composed of epitaxial GaAs and Ga ( As 0.5 P 0.5 ) films have been prepared by chemical vapor deposition. The techniques used to enhance perfection were: (a) to use film thickness below that at which misfit dislocations are formed between layers; (b) to match the lattice parameter of the substrate to the lattice parameter of the multilayer taken as a whole; and (c) to use coherency, or misfit, strain to drive threading dislocations out of the sample. Specimens prepared using these techniques contained no dislocations to accommodate misfit between layers, and few dislocations to accommodate misfit between multilayer and substrate. The density of threading dislocations was 4 ⧸ cm 2 . This is at least 10 4 times smaller than the density of threading dislocations in the multilayers described in Parts I and II. These results establish that multilayers containing few dislocations can be made from materials with rather different lattice parameters.

The structure of PbTe films grown on BaF2 by hot wall epitaxy (HWE) was studied by combined cross-sectional and plane view electron microscope observations. The main defects were low angle boundaries, (111) growth twins, and threading dislocations. No misfit dislocations were observed at the PbTe/BaF2 interface although the misfit is 4%. A mechanism which permits the relief of misfit without creation of misfit dislocations or strain is proposed.

The dominant problem in the epitaxial growth of GaAs and other III-V compounds on silicon is the problem of threading dislocations caused by the large lattice mismatch of the compound semiconductors relative to the Si substrate. Efforts to suppress these dislocations to levels as low as are routinely achieved in epitaxy on lattice-matched substrates, have fallen far short of the goal, and there are strong theoretical arguments against this possibility. However, promising devices are being achieved despite the high dislocation densities, even demanding minority carrier devices such as quantum well lasers. Dislocations threading through narrow quantum wells are evidently far less deleterious than bulk dislocations. The prospects for VLSI HBT circuits are also promising.

The relative weights of surface recombination, misfit dislocation density and threading dislocation density in the performance of a photovoltaic device are ascertained in the generation-recombination operating limit of a planar HgCdTe double layer heterostructure. In this limit, surface recombination is found to be much less important than the dislocations, while the balance between misfit and threading dislocations is determined by the relative size of the average misfit segment length and the device lateral dimension.

Dislocations in the LPE InP/InGaAsP/InP double hetero-structure are investigated by using chemical etching and optical microscope techniques. Multiplication of the threading dislocations in the third InP layer has been found from observation of etch pits revealed by the AB etch at about 60°C. Some properties of this multiplication and its origin are discussed.