Search

It has been shown that threading dislocations may be removed from patterned mismatched heteroepitaxial layers through a process of dislocation sidewall gettering (DSG), also known as patterned heteroepitaxial processing (PHeP). This gettering approach involves the glide of dislocations toward sidewalls, where they become trapped by image forces. Simple quantitative models have been developed for DSG, but they fail to explain why only partial removal of dislocations was observed in ZnSSe/GaAs (001) whereas complete removal has been achieved in ZnSe/GaAs (001) with higher lattice mismatch. Until now this phenomenon has been qualitatively explained by the presence of sessile dislocations. Here we present a quantitative model for pinning interactions and show that these interactions can limit the growth of misfit dislocation segments and thereby reduce the effectiveness of DSG in ZnSySe1-y/GaAs (001) relative to ZnSe/GaAs (001).

In addition to pure threading screw dislocations (TSDs), the presence of threading mixed dislocations (TMDs) (with a component) has been reported both in 4H-SiC axial slices (wafers cut parallel to the growth axis) and in commercial offcut wafers (cut almost perpendicular to the growth axis). In this paper, we first demonstrate a method to quickly distinguish TMDs from TSDs in axial slices via synchrotron white-beam x-ray topography. Since such axial slices are usually not available for commercial purposes, a systematic method is then developed and demonstrated here to unambiguously determine the Burgers vectors of TMDs in 4H-SiC commercial offcut wafers. In this second study, both synchrotron monochromatic-beam x-ray topography and ray-tracing simulation are used. The x-ray topographs were recorded using grazing-incidence geometry. The principle of this method is that the contrast of dislocations on different reflections varies with the relative orientation of Burgers vectors with respect to the diffraction vectors. Measurements confirm that, in a commercial offcut wafer, the majority of the threading dislocations with screw component are mixed-type dislocations.

Previous studies have shown that strain-controlled cyclic stability was maintained in bulk Cu samples with highly oriented nanoscale twins. In order to explore the underlying fatigue mechanism, transmission electron microscopy observations under two-beam diffraction condition were utilized to characterize the dislocation configurations in the twin/matrix layers of as-fatigued nanotwinned Cu. It was clarified that the threading dislocations with Burgers vector parallel to twin boundaries are mainly active during fatigue. A three-dimensional stereo projection was re-configured for demonstrating the special structure of dislocations in nanoscale twins.

In this work, significant reduction of the density of threading dislocations (TDs) in AlN epilayers grown on sapphire substrates via metalorganic chemical vapor deposition has been obtained by insertion of thin intermediate-temperature interlayers (IT-ILs). The growth temperature of the IT-ILs ranged from 750°C to 950°C after the initial growth at high temperature of 1200°C. Detailed characterizations were performed to understand the mechanisms of the reduction in dislocation density. It is found that the relatively low growth temperature of the IT-ILs can modify the originally two-dimensional (2D) growth mode to a three-dimensional (3D) growth process and creates a high density of small islands at the interface. During the subsequent growth of the high-temperature AlN layer, the AlN islands initially coalesce to form larger grains as the growth proceeds, and some TDs present in the previous AlN epilayers are found to bend near the interlayer, leading to dislocation merging and annihilation.

The design of metamorphic buffer layers for semiconductor devices with reduced defect densities requires control of lattice relaxation and dislocation dynamics. Graded layers are beneficial for the design of these buffers because they reduce the threading dislocation density by (1) allowing the distribution of the misfit dislocations throughout the buffer layer therefore reducing pinning interactions, and (2) enhancing mobility from the high built-in surface strain which helps to sweep out threading arms. In this work, we considered heterostructures involving a linearly-graded (type A) or step-graded (type B) buffer grown on a GaAs (001) substrate. For each structure type, we studied the equilibrium configuration and the kinetically-limited lattice relaxation and non-equilibrium threading dislocations by utilizing a dislocation dynamics model. In this work, we have also considered heterostructures involving a constant composition ZnS y Se1−y device layer grown on top of a GaAs (001) substrate with an intermediate buffer layer of linearly-graded (type C) or step-graded (type D) ZnS y Se1−y . For each structure type, we studied the requirements on the thickness and compositional profile in the buffer layer for the elimination of all mobile threading dislocations from the device layer by the dislocation compensation mechanism.

InSb epilayers and InSb/Al0.20In0.80Sb quantum wells were grown on Ge(001) substrates and Ge-on-insulator (GeOI)-on-Si(001) substrates by molecular beam epitaxy. Growth on both on-axis and 4°-off-axis substrate orientations was studied. Anti-phase domains were formed when InSb films were grown on on-axis substrates, but suppressed significantly by the use of 4°-off-axis substrates. Such off-axis substrates also reduced the densities of micro-twin defects and threading dislocations. The defect reduction resulted in an increase in the room-temperature electron mobility from 37,000 to 59,000 cm2/Vs in 4.0-μm-thick InSb epilayers and from 10,000 to 20,000 cm2/Vs in 25-nm-thick InSb quantum wells on Ge(001) and GeOI-on-Si(001) substrates.

GaN epilayer was grown on a new polyhedral patterned sapphire substrate (new PSS) by metal–organic chemical vapor deposition. The new PSS was prepared by combining the dry etching technique and wet etching technique. The X-ray diffraction indicated that the full width at half maximum values of (0002) and ( $$10\overline{1}2$$ ) diffraction peaks in the GaN epilayer grown on the new PSS were evidently smaller than that in the GaN epilayer grown on the normal treated PSS. The improvement of GaN quality was attributed to the reduction of threading dislocations (TDs) in GaN epilayer, and the mechanism of the reduction of TDs was analyzed. The influence of the new PSS on the optical properties as well as the residual stress in GaN epilayer was also discussed.

The structural and morphological properties of metal-organic chemical vapor deposition (MOCVD)-grown InGaN/GaN light-emitting diode (LED) structures with different In content have been studied by high-resolution X-ray diffraction (HRXRD), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), and Photoluminescence (PL). It is found that the tilt and twist angles, lateral and vertical coherence lengths (CLs) of mosaic blocks, grain size, screw and edge dislocation densities of GaN and AlN layers, and surface roughness monotonically vary with In content. Experimental results show that the mosaic block dimensions for every two layers generally increase with increasing In content, with exception of the lateral CL of the GaN layer, which exhibits an inverse behavior. In this case, the strain values and tilt angles show a decrease accordingly. At the same time, the screw dislocation densities and twist angles of the GaN and AlN layers decrease and increase monotonically, respectively. The edge dislocation density of AlN shows a decreasing behavior, while that of the GaN exhibits an increasing trend. Furthermore, LED structures display an island-like surface structure at a relatively high In composition, in contrast to a well-defined step-terrace structure at a low In composition. European UnionEuropean Commission; TUBITAKTurkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [105E066, 105A005, 106E198, 106A017]; Turkish Academy of SciencesTurkish Academy of Sciences; DPTTurkiye Cumhuriyeti Kalkinma Bakanligi [2011K120290] This work is supported by the European Union under the projects EU-METAMORPHOSE, EU-PHOREMOST, EU-PHOME, EU-ECONAM, and TUBITAK under Projects Numbers 105E066, 105A005, 106E198, 106A017. One of the authors (E.O.) also acknowledges partial support from the Turkish Academy of Sciences.; This work was also supported by the DPT under the project no. 2011K120290

The InxGa1-xN epitaxial layers, with indium (x) concentration changes between 0.16 and 1.00 (InN), were grown on GaN template/(0001) Al2O3 substrate by metal organic chemical vapour deposition. The indium content (x), lattice parameters and strain values in the InGaN layers were calculated from the reciprocal lattice mapping around symmetric (0002) and asymmetric (10-15) reflection of the GaN and InGaN layers. The characteristics of mosaic structures, such as lateral and vertical coherence lengths, tilt and twist angle and heterogeneous strain and dislocation densities (edge and screw dislocations) of the InGaN epilayers and GaN template layers were investigated by using high-resolution X-ray diffraction (HR-XRD) measurements. With a combination of Williamson-Hall (W-H) measurements and the fitting of twist angles, it was found that the indium content in the InGaN epilayers did not strongly effect the mosaic structures' parameters, lateral and vertical coherence lengths, tilt and twist angle, or heterogeneous strain of the InGaN epilayers. © 2013 Springer Science+Business Media New York.

The design of lattice-mismatched semiconductor devices requires a predictive model for strains and threading dislocation densities. Previous work enabled modeling of uniform layers but not the threading dislocations in device structures with arbitrary compositional grading. In this work we present a kinetic model for lattice relaxation which includes misfit–threading dislocation interactions, which have not been considered in previous annihilation–coalescence models. Inclusion of these dislocation interactions makes the kinetic model applicable to compositionally graded structures, and we have applied it to ZnSe/GaAs (001) and ZnSySe1−y/GaAs (001) heterostructures. The results of the kinetic model are consistent with the observed threading dislocation behavior in ZnSe/GaAs (001) uniform layers, and for graded ZnSySe1−y/GaAs (001) heterostructures the kinetic model predicts that the threading dislocation density may be reduced by the inclusion of grading buffer layers employing compositional overshoot. This “dislocation compensation” effect is consistent with our high-resolution x-ray diffraction experimental results for graded ZnSySe1−y/GaAs (001) structures grown by photoassisted metalorganic vapor-phase epitaxy.

GaN epilayers with porous SiNx interlayer and changed growth modes were grown by metal–organic chemical vapor deposition on c-plane sapphire substrates. Comparing with GaN epilayer grown by ordinary method, the crystalline qualities were significantly improved. The improvement was attributed to the reduction of the density of threading dislocations causing by over-growth process combining with delayed coalescence of individual GaN islands. The influence of the deposition and annealing of nucleation layer on the GaN regrowth was also discussed.

This study describes the elimination of threading dislocations (TDs) in GaN nanostructures. Cross-sectional transmission electron microscopy (XTEM) analysis reveals that the nominal [0001] line direction of a TD changes when it enters a GaN nanostructure and the dislocation then terminates at a sidewall facet. It is suggested that the driving force for this process is the reduction of dislocation line energy, and for a pure-edge dislocation, this TD elimination process can be accomplished simply by dislocation climb. This mechanism is active whenever a threading defect is in close proximity to a surface. Preliminary XTEM analysis of defects in AlGaN and InGaN core–shell growth onto GaN nanostructures is also shown. Although more work is required to improve the quality of core–shell InGaN epitaxial growth, nanostructures appear to offer a route to defect-free, nonpolar GaN-based devices.

Over 350 4H-SiC Schottky barrier diodes (SBDs) of varying size are characterized using current-voltage (I-V) measurements, with some also measured as a function of temperature. Devices display either a characteristic single-barrier height or atypical dual-barrier heights. Device yields are shown to decrease as device area increases. Molten KOH etching is used to highlight defects for analysis by optical microscopy and atomic force microscopy. The I-V characteristics are compared against the defect density. A positive correlation between effective barrier height and effective electrically active area of the SBDs is found. No correlation is found between threading dislocations and ideality factor or barrier height.

We have studied the use of overshoot graded layers for the control of the dislocation density in mismatched heteroepitaxial layers. Graded ZnS y Se1–y structures were grown on GaAs (001) by photoassisted metalorganic vapor-phase epitaxy (MOVPE) and characterized by high-resolution x-ray diffraction (HRXRD). All samples had a uniform top layer of ZnS0.014Se0.986, and various graded layers were incorporated between the substrate and the uniform top layer; these included forward-graded (FG) and reverse-graded (RG) buffers. Some structures incorporated overshoot at the interface with the uniform top layer (FGO and RGO buffers). Among the FG samples, those with overshoot exhibited better crystal quality and lower dislocation densities than those without. This is expected because the mismatched interface between the graded layer and the top ZnS0.014Se0.986 can affect the bending over of threading dislocations for the production of misfit dislocations, indirectly promoting annihilation and coalescence reactions. An overshoot interface with 0.1% mismatch was found to remove 2 × 108 cm−2 dislocations from the top device layer. Overshoot did not reduce the dislocation density in RG structures, but this may be because the sign of the overshoot caused the generation of new dislocations rather than interactions between existing ones. For growing a high-quality device layer with minimal defect density, it appears that steep forward-graded layers with overshoot may be best in this material system.

The characteristics of defects in HgCdTe liquid-phase epitaxy (LPE) epilayers were investigated by using Schaake’s and Chen’s etches. By tracking the etch pits (EP), two kinds of threading dislocations with and orientations were observed for the first time in HgCdTe LPE epilayers. They are ascribed to perfect 60 deg dislocation and Shockley partial screw dislocations. The kinds of dislocation etch pits revealed by Schaake’s and Chen’s etches were experimentally confirmed to be correlated one-to-one. In addition to the threading dislocation etch pits, another kind of etch pits without the threading feature was also observed using both etch methods. The density of the nonthreading etch pits increases in the regions close to epilayer-substrate interfaces, scratched areas, and melt droplets. The etch pit density (EPD) varies from 104 cm−2 to 107 cm−2 from sample to sample or at different places on the same sample, indicating that they are correlated to stresses and should be considered in the assessment of HgCdTe epilayers.

The morphology of surfaces of Pb 1−x Eu x Se epitaxial films on CaF 2 /Si(111) substrates in the initial state and after treatment by high-density inductive Ar plasma in different regimes is investigated by the methods of atomic force microscopy. It is demonstrated that threading dislocations serve as cores for the formation of large bulges during sputtering of a semiconductor material. The influence of treatment regimes on the geometrical parameters of large bulges and characteristics of the surrounding nanorelief is revealed.

The atomic and electronic structures of the c threading dislocations with an edge or screw character were compared using a tight binding formalism which takes into account charge transfer. The two dislocations do not exhibit dangling bonds. While the screw dislocation contains only constrained Ga-N bonds, the edge dislocation contains Ga-Ga and N-N wrong bonds. Both dislocations are found to induce shallow and deep gap states.

A ‘cross-hatch’ morphology is often seen in strain-relaxed Si1-xGex virtual substrates grown using the compositional grading technique. High resolution channeling contrast microscopy measurements, which probe both laterally and vertically into the structure, have revealed the association of such cross-hatch patterns with local lattice-plane bending. In this work, we report the influence of the growth temperature on the extent of the local lattice tilts determined from the channeling contrast measurements. Lines of pileup threading dislocations observed on the surface have also been imaged for the first time, providing us with information on their influence on the lattice-tilt arrangements and orientations.

The dislocation configurations in SrTiO3 thin films grown epitaxially on LaAlO3 (100) substrates were studied by conventional and high-resolution transmission electron microscopy. Misfit dislocations had, in most cases, a Burgers vector a〈100〉 and line directions of 〈100〉 These dislocations constitute orthogonal arrays of parallel dislocations at the interface, relieving the lattice mismatch between SrTiO3 and LaAlO3. Threading dislocations were found to be the major defects in the films. Two types of threading dislocations with the Burgers vectors a〈100〉?and a〈100〉?were identified. The relations of these threading dislocations with the misfit dislocations were investigated and are discussed in this paper.

Two types of threading dislocations with edge components were investigated by a high-resolution transmission electron microscope in undoped GaN epilayers grown on Al2O3 substrates. One is a fully filled core with regular contraction and stretch of bright dots, and the other is incompletely filled with one bright dot less and irregular contraction and stretch of bright dots. The bright dots were distorted and degenerated into bright line segments at cores in areas with smaller local dislocation intervals. The calculated results suggested that the distorted bright regions are attributable to the glide and/or climb caused by nearby dislocation interactions.

GaN grown on sapphire (α–Al2O3) was characterized by laser-induced molecular beam epitaxy. Threading dislocations with Burgers vectors of 1/3〈1120〉, 1/3〈1123〉 and [0001] were observed with a predominance of the first type. Additionally, inversion domains with Ga-polarity existed with respect to the adjacent matrix, which was of N-polarity. The dislocation densities and coherence lengths were deduced from x-ray diffraction and found to be in accordance with those measured by transmission electron microscopy. Both displacement fringe contrast analysis and high-resolution transmission electron microscopy results indicated that the inversion domain boundaries had Ga–N bonds between domains and the adjacent matrix.

Strain relaxation of hypercritical thickness InxGa1−xAs layers has been observed during lateral oxidation of underlying AlAs layers. Strain relaxation of InxGa1−xAs layers was studied as a function of indium composition and the AlAs oxidation temperature. It is proposed that the enhanced strain relaxation is due to two factors. The first is enhanced motion of threading dislocations due to stresses generated during the lateral oxidation process. The second is the porous nature of the InxGa1−xAs/Al2O3 interface that minimizes the interaction of threading dislocations with existing misfit dislocation segments. The extent of strain relaxation increases with increasing oxidation temperature, whereas the efficiency of strain relaxation was found to decrease with increasing indium composition. The efficiency of strain relaxation upon oxidation can be improved by reducing the misfit dislocation density at the InxGa1−xAs/AlAs interface prior to oxidation and by changing the nature of the InxGa1−xAs/Al2O3 interface.

An approach is proposed to understand the role of relaxation enhancing interlayers in the evolution of threading and misfit dislocations in growing lattice mismatched films. The approach based on the ability of misfit dislocations to reduce their local stresses due to the influence of relaxation enhancing interlayers. The diminishing of these local stresses eliminates blocking effect of misfit dislocations and allows efficient motion of threading dislocations with consequent overall strain relaxation in the heteroepitaxial film. An analytical model is developed which quantitatively describes the dislocation density changes during growth with relaxation enhancing interlayers. The applications of the approach to lattice engineered substrates (exploring the techniques of internal oxidation) and weakly bonded compliant layers are discussed.

As the number of bands and the complexity of HgCdTe multicolor structures increases, it is desirable to minimize the lattice mismatch at growth interfaces within the device structure in order to reduce or eliminate mismatch dislocations at these interfaces and potential threading dislocations that can degrade device performance. To achieve this we are investigating the use of Hg1−x−yCdxZnyTe quaternary alloys which have an independently tunable lattice constant and bandgap. Lattice matching in Hg1−x−yCdxZnyTe structures can be achieved using small additions of Zn (y

The behavior of threading dislocations during mass transport of GaN was investigated in detail by transmission electron microscopy. Mass transport occurred at the surface. Therefore, growing species are supplied from the in-plane direction. The behavior of threading dislocations was found to be strongly affected by the mass transport process as well as the high crystallographic anisotropy of the surface energy of the facets particular to GaN.

GaN technology relies on highly mismatched heteroepitaxial growth, mainly on sapphire or SiC substrates, and therefore suffers from 109 to 1010 threading dislocations per cm2. The origin and the deteriorating influence of the extremely high dislocation densities are analyzed with regard to the specific circumstances of GaN technology. Various attempts to cope with heteroepitaxial growth are discussed, from the use of nucleation layers to the growth on GaN single bulk crystals. Special focus is put on the impact of the approaches on the device performance.

In situ transmission electron microscopy (TEM) was performed to study dislocation motion during temperature cycles in aluminum films passivated with a SiO2 layer. The films were cycled from room temperature to 450 °C. Wedge-haped cross-sectional TEM samples were used to retain the constraint of the Si substrate. Besides interactions between dislocations and interfaces, the movement of threading dislocations within the constrained aluminum film was observed. This observation provides an experimental corroboration of the occurrence of threading dislocation motion, which is the basis for rationalizing the high-ield strength of thin films in available models of thin-film plasticity.

Within the framework of strong-coupling theory we study the effect of highly negatively charged threading dislocations on the electron mobility collapse in n-GaN layers. An analytical expression is derived showing the way in which the electrically active dislocations establish the critical carrier concentration at which the collapse occurs. Results are presented suggesting that the experimental collapse data can be utilized for determining the characteristic magnitude of the statistical filling factor of dislocation related traps in the GaN bandgap.

We have shown that threading dislocations can be removed from patterned heteroepitaxial semiconductors by glide to the sidewalls, which is driven by the presence of image forces. In principle, it should be possible to attain highly mismatched heteroepitaxial semiconductors which are completely free from threading dislocations, even though they are not pseudomorphic, by patterned heteroepitaxial processing. There are two basic approaches to patterned heteroepitaxial processing. The first involves selective area growth on a pre-patterned substrate. The second approach involves post-growth patterning followed by annealing. We have developed a quantitative model which predicts that there is a maximum lateral dimension for complete removal of threading dislocations by patterned heteroepitaxy. According to our model, this maximum lateral dimension is proportional to the layer thickness and increases monotonically with the lattice mismatch. For heteroepitaxial materials with greater than 1% lattice mismatch, our model predicts that practical device-sized threading dislocation-free regions may be realized by patterned heteroepitaxial processing.

The initial nucleation of GaSb on (001) GaAs substrates by metalorganic vapor phase epitaxy has been investigated using transmission electron microscopy (TEM) and high resolution electron microscopy (HREM). TEM results showed that the GaSb islands experience a morphological transition as the growth temperature increases. For growth at 520°C, the islands are longer along the [110] direction; at 540°C, they are nearly square, and at 560°C, they are longer along the $$[\bar 110]$$ direction. Possible mechanisms are proposed to describe such a transition. TEM and HREM examination showed that lattice misfit relaxation mechanisms depend on the growth temperature. For the sample grown at 520°C, the lattice mismatch strain was accommodated mainly by 90° dislocations; for the sample grown at 540°C, the misfit strain was relieved mostly by 90° dislocations with some of 60° dislocations, and for the sample grown at 560°C, the strain was accommodated mainly by 60° dislocations which caused a local tilt of the GaSb islands with respect to the GaAs substrate. The density of threading dislocations was also found to be dependent on the growth temperature. Mechanisms are proposed to explain these phenomena.

The (110)-oriented misfit dislocation density reduction in the growth of Inx Gal−xAs (x-0.06) heterostructure on GaAs (001) substrate patterned with circular mesas has been observed with X-ray double-crystal topography. It has been found that, depending on the InGaAs thickness on the mesa sidewall, there is athreshold which inhibits the glide of threading dislocations through the mesas. No misfit dislocations are observed terminating on the top of the mesas. The experimental results obtained here are explained by the resistant effect of mesas from the point of view of the elastic strain energy of thepatterned region.

The effect of plasma exposure to n-type GaN surfaces has been examined. Etch pits are formed as a result of preferential sputtering at the sites of threading dislocations. Dark spots which are visible before plasma exposure can be attributed to screw dislocations, while those that emerge after plasma exposure are edge dislocations. The optimum condition for revealing defects clearly is derived, and has been adopted for the study of dislocations in a series of GaN epilayers grown under different conditions. A distinct trend in the dislocation density can be observed as the dopant concentration of the film varies.

Molecular beam epitaxy (MBE) grown GaAs films on Si substrates (0 0 1) 4° off towards 〈1 1 1〉 A and towards 〈1 1 1〉 B, were examined by means of transmission electron microscopy (TEM). The results indicate that in both samples, threading dislocations in the GaAs epilayer are blocked mainly in a thin layer near the GaAs-Si interface. This thin layer is like an inner interface, consisting of pyramidal islands and is flatter on the As growth surface than that on the Ga growth surface. In the type B sample, the density of dislocations is lower, the inner interface is flatter and the number of twins is much larger than that in the type A sample.

This paper reports enhanced internal-quantum-efficiency (IQE) in InGaN-based multi-quantum-well (MQW) grown on Si(111) substrate with underlying strained-layer-superlattice (SLS) cladding layer for application in LDs and LEDs. In comparative study between a thick Al0.03Ga0.97N bulk and an Al0.06Ga0.94N/GaN SLS cladding layer, transmission-electron-microscopy (TEM) images reveal that Al0.06Ga0.94N/GaN SLS cladding layer is effective to suppress threading dislocations. A higher IQE has been achieved in sample with underlying Al0.06Ga0.94N/GaN SLS cladding layer, compared to that of Al0.03Ga0.97N bulk cladding layer. IQE of 31.6% has been achieved in sample with underlying Al0.06Ga0.94N/GaN SLS cladding layer when the MQW thickness is reduced to 2 nm.

Using transmission electron microscopy, we have analyzed dislocations in AlN nucleation layers and GaN films grown by metallorganic chemical vapor deposition (MOCVD) on the (0001) surface of epitaxially-grown 4H-SiC mesas with and without steps. For 4H-SiC substrates free of SiC surface steps, half-loop nucleation and glide parallel to the AlN/SiC interfacial plane play the dominant role in strain relief, with no mechanism for generating threading dislocations. In contrast, 4H-SiC mesa surfaces with steps give rise to regions of high stress at the heteroepitaxial interface, thereby providing an environment conducive to the nucleation and growth of threading dislocations, which act to accommodate misfit strain by the tilting of threading edge dislocations.

Experimental measurements in epitaxial semiconductor deposits of the critical thick-ness above which misfit dislocations are generated may differ substantially from values calculated from early models that are successful for metallic deposits. The early models of misfit dislocation generation based on a glide mechanism for threading dislocations have been modified to include frictional forces on threading dislocations. The modified model can account for the critical thickness in both metal as well as semiconductor epitaxial deposits. It results in a residual stress that is not relaxed even at large deposit thicknesses. The influence of the frictional forces is diminished at large misfits.

We report the observation of threading dislocation de-multiplication process by transmission electron microscopy (TEM). The GaN films used in this study were grown on (0001) sapphire substrates with LT-GaN buffer layers by reduced pressure organometallic vapor phase epitaxy. By using g · Db = 0 invisibility criterion, it was found that some of TDs were de-multiplicated by interactions among themselves. In particular, type a+c TDs were found to nucleate through the interactions between type a and type c TDs in GaN near the GaN/sapphire interface so that the de-multiplication of TDs in GaN films was achieved.

Defect-free germanium has been demonstrated in SiO2 trenches on silicon via aspect ratio trapping, whereby defects arising from lattice mismatch are trapped by laterally confining sidewalls. Results were achieved through a combination of conventional photolithography, reactive ion etching of SiO2, and selective growth of Ge as thin as 450 nm. It was revealed that facets, when formed early on in the growth process, play a dominant role in determining the configurations of threading dislocations in the films. This approach shows great promise for the integration of Ge and/or III-V materials, sufficiently large for key device applications, onto silicon substrates.

Growth of AlN on 4H-SiC (11-20) substrates by plasma-assisted molecular-beam epitaxy is presented. Very high-quality AlN can be grown under a slightly Al-rich condition. Transmission electron microscopy revealed that the AlN layer has 4H crystalline structure with high-phase purity (stacking-fault density is 5×106cm−1) and the density of threading dislocations is as small as 8×107cm−2.

We report the photoluminescence characteristics of fresh dislocations introduced by the plastic deformation in GaN bulk crystals. GaN crystals prepared from free standing wafers grown by the HVPE technique were compressed plastically at 900 to 1000°C. In the deformed crystals (a/3) (1120) dislocations on the (1110) prismatic plane, corresponding to the so-called threading dislocations, were observed in TEM. In the PL studies at 11K the intensity of the near band-edge luminescence decreased drastically in the deformed GaN by about 1/12 than that of the as-grown GaN, which seems to imply the introduction of a high density of non-radiative reco!m bination centers into GaN! during the plastic deformation. By the plastic deformation the yellow band luminescence decreased remarkably meanwhile the red band and other new luminescence developed relatively. It is found that dislocations do not originate to the yellow luminescence but the red luminescence.

Structural defects affecting the lifetime of GaN-based laser diodes (LDs) on epitaxial lateral overgrown (ELO) GaN layers have been investigated. Almost all of the threading dislocations that appeared in the wing regions have edge character, whereas the dislocations at the coalescence boundaries have both edge character and mixed character. The origins of the threading dislocations in the wing regions are the lateral extension of dislocations from the seed regions that contingently bend upwards to the epi-surface. Thus, edge dislocations are most considerable threading dislocations in GaN-based LDs on ELO GaN layers, since the laser stripes are fabricated in the wing regions. In the degraded LDs, neither dislocation multiplication from the threading dislocations nor any structural changes of the threading dislocations were observed. This indicates that degradation is not caused by dislocation multiplication at the active layers, which is usually observed in LDs featuring zincblende-based structures. Although the threading dislocations in the LD stripes do not multiply during device operation, our degradation experiments revealed that the lifetime of the GaN-based LDs depends on the dislocation density. The degradation rate was almost proportional to the square root of the aging time. Our results indicate that degradation is governed by a diffusion process, and a detailed degradation mechanism is proposed.

A new method for highlighting defects in thin Si/SiGe layers is used to investigate the densities of various types of defects present in strained Si layers grown on relaxed SiGe layers. Defect densities were measured in strained Si layers formed on graded SiGe buffer layers (bulk), as well as silicon germanium-on-insulator substrates (SGOI), from both external and internal sources. The result of this investigation indicates that in addition to threading dislocations (TDs) and dislocation pile-ups, planar defects, i.e., stacking faults, are present in all but one of the materials studied. Due to the larger crystalline area affected by these planar defects, citation of only TD density as an indication of material quality is inadequate. A better measure of crystalline quality should include the density of TDs, pile-up clusters and planar defects (stacking faults) as well as some indication of the length distribution of the pile-ups and stacking faults.

Cubic silicon carbide (3C-SiC) is a suitable semiconductor material for high temperature, high power and high frequency electronic devices, because of its wide bandgap, high electron mobility and high saturated electron drift velocity. The usage of Si substrates has the advantage of large area substrates for the growth of 3C-SiC layers. However, large lattice mismatch between 3C-SiC and Si (>20%) has caused the generation of defects such as misfit dislocations, twins, stacking faults and threading dislocations at the SiC/Si interface. Lateral epitaxial overgrowth (ELOG) of 3C-SiC on Si substrates using SiO2 has been reported to reduce the defect density. In this report, epitaxial growth of 3C-SiC on T-shape patterned (100) Si substrates has been investigated to reduce interfacial defects.

The effects of silicon-doping on the microstructure of Al0.07Ga0.93N/GaN multiple-quantum-well (MQW) have been studied by TEM. Significant changes of surface morphology and dislocation core structures have been observed due to Si-doping in the Al0.07Ga0.93N barriers. Threading dislocations create surface pits in the MQW as a result of Si doping. With an increasing doping level, the pits change the shape from small faceted pyramid to large cone. The formation mechanism of the surface pits has been discussed from both dynamics and kinetics points of view. We have also observed nanopipes constrict to form closed core screw dislocations in the MQW due to Si-doping.

Plan-view and cross-section samples of (1120) (a-plane) GaN grown on 4H-SiC substrates with AlN buffer layers were studied by transmission electron microscopy. Samples reveal the presence of a high density of stacking faults formed on the basal plane of hexagonal GaN. These stacking faults, terminated in the growth plane by threading dislocations, nucleate at the AlN/4H-SiC interface and propagate to the GaN layer surface. High resolution electron microscopy shows that the majority of stacking faults are low-energy planar defects of the type I1and I2. High energy stacking faults (E) are not observed.

Epitaxial Ba0.6Sr0.4TiO3 films were grown onto (001) LaAlO3 by pulsed-laser deposition, and the dislocation structures of the films were investigated using transmission electron microscopy. Misfit dislocations with a periodicity of about 7 nm and Burgers vectors b = a were observed at the interface. High densities of threading dislocations was present in the films with Burgers vector b = a. The observations reveal that threading dislocations are not generated as the result of half-loop climb from the deposit surface as proposed previously, but are instead formed when misfit dislocations are forced away from the interface during island coalescence.

The density of vertical threading dislocations at the surface of GaN grown on sapphire by cantilever epitaxy has been reduced with two new approaches. First, narrow mesas (7/cm2 was achieved by combining these two approaches. We also suggest other developments of cantilever epitaxy for reducing dislocations in heteroepitaxial systems.

Growth of pendeo-epitaxial (PE) layers introduces misorientation between the seed layers and the overgrown wing layers. The origin of this misorientation has been studied by Transmission Electron Microscopy (TEM) using a set of samples in which subsequent procedures utilized in PE were applied, i.e. growth of GaN template, stripe etching, annealing at the growth temperature of the PE layers and final PE growth. It was shown that etching of seed-stripes did not change the type of defects or their distribution. However, heating to the PE growth temperature drastically modified the surface and V-shaped pits were formed. The surface became smooth again after the PE growth took place. Overgrowth of the V-shaped pits resulted in formation of edge threading dislocations over a seed-stripe region with a dislocation density of 8.0×108 cm−2. Formation of new edge dislocations over the seed can have an influence on the misorientation between the PE grown regions.

Three possible situations of extended defect formation during sublimation growth of SiC have been investigated: a-plane growth, occurrence and effect of irregular growth interfaces, and development of elongated open volume morphological defects. While in the first case the most preferred defects are basal plane stacking faults (SFs), in other studied samples threading dislocations and high energy SFs have been revealed, these suggesting stress accumulated in the course of the growth process. Formation of morphological defects of the above character has been observed in the presence of micropipes and step flow growth mode on vicinal surfaces. Growth on atomically flat surfaces can eliminate this type of defects but the polytype uniformity is more difficult to maintain.

The defect structure of a 350-nm-thick epitaxial Ba0.3Sr0.7TiO3 thin film grown on (001) LaAlO3 has been investigated using conventional and high-resolution transmission electron microscopy. The predominant defects in the film are threading dislocations (TDs) with Burgers vectors b = and . A high density of extended stacking faults (SFs) with displacement vectors R = (1/2) were also observed in the near-interface region of the film. The faults are associated with dissociated dislocations and partial halfloops. Some findings about dislocation dissociation and the atomic structure of the (1/2) faults are observed for the first time in perovskites to our knowledge. The mechanisms for the generation, dissociation and evolution of the TDs as well as for the formation mechanism of the SFs are discussed.