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We have systematically investigated highly mismatched AlInSb photodiodes grown on GaAs substrates operating in the mid-infrared range. A novel characterization method was introduced to analyze the recombination mechanism within an active layer of the devices, which revealed a high conductance stemming from the leaky behavior of dislocations. The introduction of a dislocation filter layer successfully reduced threading dislocations and improved resistance area product of photodiodes, leading to high detectivity at room temperature.

Basal-plane and threading dislocations in multipoint-seed Na-flux-grown GaN single crystals are characterized in terms of Burgers vectors mainly by using bright-field X-ray topography under multiple-diffraction conditions. The technique, combined with a CMOS camera system with high spatial resolution, can provide topographic images of the dislocations with a relatively high dislocation density (up to approximately 5×105cm−2). It is possible to directly determine the Burgers vector of individual dislocations based on invisibility criteria. From the present experiment, it is found that almost all basal-plane dislocations have a-type Burgers vectors, and threading dislocations have a- and (a + c)-type Burgers vectors.

In this work, we give a direct interpretation of micrographs of the 60° and 90° defect core at the GaAs/Si interface using aberration corrected scanning transmission electron microscopy. We investigate the post-growth annealing effects on dislocation rearrangement at the interface as well as the threading dislocations in buffer layers; finally, the density of threading dislocations has been calculated as a function of annealing temperature.

The defect structure of a 350-nm-thick epitaxial Ba0.3Sr0.7TiO3 (BSTO) film grown on (001) LaAlO3 has been investigated using conventional and high-resolution transmission electron microscopy. The dominant defects in the film are edge-type threading dislocations (TDs) with Burgers vectors b=〈100〉 and 〈110〉. Pure-screw TDs and partial TDs of mixed character were also observed. A rapid reduction of defect density occurred after the growth of the first 100 nm BSTO adjacent to the interface. In the top layer of the film, all TDs with b=〈100〉 are perfect while those with b=〈110〉 are usually dissociated into two partials with a small separation (a few nanometers). However, in the near-interface layer of the film, many TDs with b=〈100〉 are split into two or three partials. A high density of extended stacking faults with displacement vectors of 12〈110〉 type were observed. The stacking faults are associated with dissociated dislocations and partial half loops. The mechanisms for the generation, dissociation and ev...

We have demonstrated the patterned heteroepitaxial processing (PHP) approach for the removal of threading dislocations (TDs) from ZnSe and ZnS0.02Se0.98 on GaAs (001). PHP involves the growth of a continuous heteroepitaxial layer followed by postgrowth patterning and annealing. We found that the basic mechanism of TD removal by PHP is thermally activated dislocation motion in the presence of sidewalls. By studying the temperature dependence we showed that the activation energy for the annealing process (∼0.7 eV in ZnSe on GaAs) is consistent with dislocation motion by glide. We showed that there is a minimum mesa thickness required for the complete removal of TDs by PHP (∼3000 A for 70 μm×70 μm mesas of ZnSe on GaAs). This is because the lateral forces acting on TDs are proportional to the mesa thickness. We also conducted a preliminary study of the mismatch dependence of PHP. Our results suggest that PHP removes TDs more effectively in the higher lattice mismatch system ZnSe/GaAs (001) than in the lower ...

We report on the growth of near-minimum bandgap (0.1 eV) bulk InAs0.54Sb0.46 on GaAs with pronounced photoluminescence. Combining strain-mediating techniques effectively manages the ∼10% lattice mismatch. An interfacial misfit (IMF) dislocation array allows a GaAs substrate and a GaSb buffer layer to act as a direct substitute for a conventional GaSb substrate. We further increase the lattice constant with a linearly graded metamorphic buffer layer of AlGaInSb, upon which we grow an AlInSb virtual substrate with the targeted lattice constant of the active InAsSb region. We observe that the graded buffer not only manages the mismatch between GaSb and InAsSb but also reduces the density of residual threading dislocations from the GaSb/GaAs IMF by a factor of ∼10×. Material characterization demonstrates the viability of using the coupled approach of metamorphic, graded buffers and IMF arrays to manage the large lattice mismatch between the substrate and the mixed group V ternary InAsSb.

The effects of growth temperature, substrate offcut, and dislocation pileup formation on threading dislocation density (TDD) in compositionally graded SiGe buffers are explored. To investigate dislocation glide kinetics in these structures, a series of identical samples graded to 30% Ge were grown at temperatures between 650 and 900 °C on (001)-, (001) offcut 6° towards an in-plane 〈110〉-, and (001) offcut 6° towards an in-plane 〈100〉-oriented Si substrates. The field threading dislocation density (field TDD) in the on-axis samples varied exponentially with temperature, from 3.7×106 cm−2 at 650 °C to 9.3×104 cm−2 at 900 °C. The activation energy for dislocation glide in this series, calculated from the evolution of field TDD with growth temperature, was 1.38 eV, much lower than the expected value for this composition. This deviation indicates that strain accumulating during the grading process at low growth temperatures is forcing further dislocation nucleation, resulting in a deviation from pure glide-limited relaxation. The TDD of samples grown on offcut substrates exhibited a more complicated temperature dependence, likely because films grown on offcut substrates have an increased tendency towards saturation in dislocation reduction reactions at high temperature. Dislocation reduction processes were further explored by initiating compositional grading up to 15% Ge at 650 °C and continuing the grade to 30% Ge at 900 °C. The low temperature portion of this growth provided an excess concentration of threading dislocations which could subsequently be annihilated during the high temperature portion of the growth, enabling a comparison of reduction rates for different substrate offcuts. Combining these results with threading dislocation densities in a variety of other samples, a complete picture of strain relaxation kinetics in compositionally graded SiGe/Si emerges. Generally, strain relaxation in these structures is limited by dislocation glide, and threading dislocation densities are independent of final Ge content. However, we theorize that dislocation pileup formation inhibits the strain relaxation process and is therefore accompanied by a rise in field threading dislocation density. Based on these results, we now have a predictive model for TDD in compositionally graded SiGe/Si over a wide range of growth conditions.

We have studied the effects of inserting Si/Si0.6Ge0.4 strain-balanced superlattices (SLs) into Si0.8Ge0.2 (001) virtual substrates. The SiGe SL layer thickness chosen was larger than the critical thickness for elastic relaxation and generated numerous hemicylindrical features oriented along the 〈100〉 directions. These features lead, when covered by Si0.8Ge0.2, to a disruption of the well-ordered surface crosshatch along the 〈110〉 directions, and to a significant lowering of the surface roughness. There is also evidence for some filtering of the threading dislocations by the SL.

Experimentally it has been found that twist bonding a thin layer of epitaxially grown material to a thick substrate of the same material has the properties of being compliant with respect to the growth of a heteroepitaxial layer onto the thin layer. The benefit of the compliant substrate is that the heteroepitaxial layer is of much higher perfection when compared to the same growth but on a bulk substrate, primarily due to a very low density of threading dislocations present in the heteroepitaxial deposit. This concept has been investigated experimentally and discussed in terms of what is the operative mechanism of the compliant substrate. However, there is still much to be explained about the mechanism by which the compliant substrate accommodates misfit between itself and the heteroepitaxial layer. How the structure of the interface between the compliant substrate and the thick substrate can be tailored to derive the maximal benefit in the epilayer is the subject of the present article. The importance o...

Numerical simulations are used to study various dislocation interactions expected to occur when a strained epitaxial layer relaxes. Frank–Read sources located on parallel glide planes are shown to produce elaborate network patterns of dislocations in the unstrained substrate of the layer. These are strikingly similar to experimentally observed patterns in high-quality relaxed SiGe layers grown by low-temperature ultrahigh vacuum chemical vapor deposition. Frank–Read sources on intersecting glide planes, on the other hand, produce characteristic corner-pileup structures which have previously been attributed to a “modified” Frank–Read source mechanism. The blocking of threading arms by misfit dislocations is found to occur only very near the critical strain. A much more important mechanism preventing ideal layer relaxation appears to be the formation of immobile pairs of threading dislocations on parallel glide planes.

The initial stages of molecular beam epitaxy of GaSb on highly mismatched GaAs(001) substrates were investigated. Transmission electron microscopy was used to analyze the defect structure in GaSb islands and at their interfaces with GaAs(001) at different stages of growth. Based on experimental observations, we propose that the semiperiodic net of 90° misfit dislocations at the GaSb/GaAs(001) interface nucleate homogeneously at the leading edges of advancing {111} planes. After nucleation, they glide inwards along the interface plane to reach their equilibrium position. Threading dislocations in GaSb layers were directly correlated with the misfit dislocation net. We demonstrate that there are no threading defects in GaSb islands when their interfaces consist solely of 90° misfit dislocations, and that threading dislocations in the GaSb epilayer are all associated with minority 60° misfit dislocations nucleated in growing islands. The number of threading dislocations per unit area of the GaSb film is found to be independent of GaSb coverage, indicating that island coalescence does not substantially increase the number of 60° dislocations.

A scheme is presented for the reduction of threading dislocation densities in InxGa1−xAs/GaAs epitaxial single layers by accurate control of layer thickness. The model developed differs from previous models since the InxGa1−xAs growth is restricted to less than ten times the Matthews and Blakeslee critical thickness (hc) where the asymmetry in the [110] and [110] dislocation densities is the greatest. Beyond this thickness it is shown that the removal or annihilation of threading dislocations in the epilayer is more than offset by the introduction of new threading dislocations from spiral and Frank–Read‐type sources. Maintaining epilayer thickness below this thickness ensures that the majority of misfit dislocations generated lie predominantly in only one of the 〈110〉 directions, reducing the likelihood of blocking with orthogonal dislocations, thereby increasing the mean free path from that expected in higher density dislocation arrays. Etch pit densities show that the threading dislocation density can ...

The use of high-growth-temperature GaAs spacer layers is demonstrated to significantly enhance the performance of multilayer InAs/GaAs quantum-dot solar cells. Threading dislocations are observed for a 30-layer quantum-dot structure with GaAs spacer layers grown at low temperature (510°C). The formation of threading dislocations is suppressed by growing the GaAs spacer layer at high temperature (580°C), leading to enhanced quantum-dot optical and structural characteristics. Incorporation of the high-growth-temperature GaAs spacer layers into a 30-layer InAs/GaAs quantum-dot solar cell results in a dramatic increase in the short-circuit current compared to the one without the high-growth-temperature spacer layers and an increase in the short-circuit current compared to the reference GaAs solar cell. © 2012 American Institute of Physics.

Relaxed Si0.7Ge0.3 epitaxial layers that possess threading defect densities as low as 5×105 cm−2 have been grown on Si substrates by rapid thermal chemical vapor deposition. The layers were formed in a series of steps of constant Ge content, each step with either 6% or 3% more Ge than the previous one. At the low average grading rates investigated, the number of steps used to reach 30% Ge only slightly affected the density of individual threading dislocations, imaged by electron beam induced current (EBIC). However, the density of dark‐line defects seen in EBIC, which are formed from pile‐ups of threading dislocations, was strongly influenced only by the average grading rate. Both the dark line density and the dark spot density must be considered when assessing the surface of these relaxed layers.

At various doping concentrations of Si in GaN films, the correlation between the type of dislocations and photoluminescence (PL) characteristics was investigated. A different broadening behavior of symmetric and asymmetric Bragg peaks as a function of carrier concentration provided qualitative evidence that the type of threading dislocations generated in GaN layers was strongly dependent on the doping levels of Si. PL spectra in conjunction with x-ray rocking curve measurements suggested that the yellow luminescence associated with deep levels was more strongly related with edge dislocations than screw or mixed ones.

We have investigated the effect of the initial growth mode on the structural quality and dislocation configuration in epitaxial ZnSe/GaAs(100). We find that a three‐dimensional initial growth mode strongly degrades the crystal quality and results in a high density of threading dislocations and short misfit dislocation segments. On the other hand a two‐dimensional growth mode, achieved by a Zn exposure treatment of GaAs surfaces, results in few threading dislocations and long misfit dislocations. These differences are explained by postulation of new dislocation generation sites created by island coalescence.

The conditions for operation of two multiplication mechanisms in strained layers are analyzed. These are spiral and Frank–Read type sources. It is shown that a minimum thickness is required for their operation, of the order of four times the critical thickness for the bending over of threading dislocations. The implications for strain relief of mismatched layers are discussed.

A systematic study, investigating the effects of strained‐layer superlattices (SLSs) on threading dislocations present in GaAs/Si heteroepitaxial layers, was conducted. Transmission electron microscope contrast analysis was performed on ∼1% lattice‐mismatched GaAs0.72P0.28/GaAs SLSs grown on GaAs/Si substrates.Threading dislocations were found to have Burgers vectors inclined to the GaAs/Si interface. Individual strained layers ranging in thickness from 100 to 250 A were observed to have negligible effect on dislocation bending. Instead, dislocation bending occurred primarily at the first and last interfaces of the SLS packets. Similarly, effective dislocation bending was observed using 1000 A layers. Threading dislocation density close to the GaAs/Si heterointerface was found to depend on the SLS packet proximity to the interface.

The generation and propagation of threading dislocations in GaAs grown on Si was studied by transmission electron microscopy. This study was conducted by analyzing dislocation structures in GaAs at various growth stages. The dislocation structure changes as the GaAs grows from initial islands to a thick film. These changes are explained by the following physical processes: (1) nucleation of dislocations in GaAs islands, (2) generation and propagation of threading dislocations during coalescence of initial GaAs islands and their subsequent growth, and (3) bending of threading dislocations under misfit‐strain force and their interactions. The second process results in threading dislocations extending from the interface to the surface in thin films. The third process causes an improvement in near‐surface quality in thick films. The iplication of this study in confining threading dislocations to near the interface is discussed.

The defects and strain of GaN(0001) films as virtual substrate on Si(111) with step-graded Sc2O3(111)/Y2O3(111) buffers were investigated by means of transmission electron microscopy. The misfit dislocation network identified in the interfaces nearly fully compensates the lattice mismatch. Inversion domains and pinholes occur within the closed GaN film. The atomic structure of the inversion domain boundaries is identified. Major parts of the films were found to be N-polar. Threading dislocations were formed as remains from the coalescence of initial GaN islands. Furthermore, the formation of small cubic inclusions is found to be restricted to the vicinity of the interface only.

We show a strong relationship between CuPt atomic ordering and misfit dislocation glide plane preference during strain relaxation. A miscut substrate creates an asymmetry in the resolved mismatch stress between {111} glide planes, causing a preference for one glide plane that results in a systematic tilt of the epilayer relative to the substrate. However, a small degree of ordering leads to nearly 100% of dislocation glide on planes opposite to the expected planes from the substrate miscut. This result is explained as a consequence of the asymmetry between {111} glide planes of CuPt-ordered material. Lowering the ordering parameter by changing bulk composition results in a change in glide plane distribution and is accomplished through the formation of new dislocations. Control of the glide plane distribution is therefore possible by controlling the ordering parameter on a vicinal substrate. Knowledge and control of this relaxation mechanism is important for the reduction of threading dislocations in latti...

The crystal qualities of InAlN nearly lattice-matched (LM) to GaN with different thicknesses have been investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). It was found that the crystal quality of InAlN starts to degrade when the InAlN thickness exceeds several hundred nanometers, forming a structure consisting of two sub-layers with one sub-layer coherent to GaN and the other being degraded. Moreover, the degradation was found to be governed by the threading dislocations (TDs) propagation from the underlying GaN layer, rather than by the misfit strain between InAlN and GaN. Based on TEM observations, the growth evolution of the two-sub-layer structure is proposed, which is different from those conventional mechanisms of crystal-quality degradation in heteroepitaxial material. The results of InAlN nearly LM to GaN are suggested to be helpful in understanding the growths of lattice-mismatched systems of other In-contained III-nitrides, including InGaN/GaN.

Threading dislocations that are of a type were observed to form locally in InGaN layers and wells containing 7%–15% indium. Direct correlations between a type dislocations and stacking faults in InGaN layers and wells were observed. The formation of these dislocations is attributed to the dissociation of Shockley partials bounding the stacking faults.

Threading dislocations (TDs) in 4H-SiC epilayers have been investigated by means of micro-photoluminescence (μ-PL) mapping at room temperature. Enhanced nonradiative recombination at TDs was confirmed experimentally, resulting in a reduced local PL emission intensity in the μ-PL intensity map performed at 390 nm (near band-edge emission). The behavior of nonradiative recombination at TDs depends on the dislocation type: the screw type of TDs shows stronger effect on the nonradiative recombination activity than the edge type, evidencing a larger local reduction of PL emission intensity. Furthermore, the contrast of TDs in the μ-PL intensity map greatly depends on the carrier lifetimes of the 4H-SiC epilayers. Lifetimes longer than 0.5 μs are essential to obtain a discernible contrast for the individual TDs.

The detrimental effects of structural defects, micro-twins (MTs) and threading dislocations (TDs), on electron mobility have been investigated for InSb quantum wells (QWs) at room temperature (RT). The constants that are necessary to calculate the electron-mobility limits of these defects were determined by a least-squares-based method that has an advantage of clear representation of the analytical results in a two-dimensional space. Based on a mathematical consideration, a general method of converting electron-mobility limits into percentage impacts upon the total electron mobility was developed. Percentage-mobility-impact analyses showed that, when InSb QWs grown on on-axis (001) GaAs substrates have a TD density of 8.7 × 108 – 3.2 × 109/cm2, 21–14 and 18–45% of electron-mobility degradation are attributed to MTs and TDs, respectively, at RT. The use of 2° off-axis (001) GaAs substrates reduces MT densities in InSb QWs, resulting in a suppression of the MT mobility impact to 3–2% and a complementary sli...

The microstructural properties of a GaN layer grown on a patterned sapphire substrate (PSS) were studied in detail using transmission electron microscope techniques to determine dislocation and growth behaviors. Regular and uniform recrystallized GaN islands were observed on the protruding pattern. On a flat sapphire surface, the crystallographic orientation relationship of ⟨1¯21¯0⟩GaN on FS//⟨11¯00⟩sapphire and {11¯01}GaN on FS//{12¯13}sapphire existed between the GaN and the substrate. On the other hand, the orientation relationship of ⟨1¯21¯0⟩GaN layer//⟨1¯21¯0⟩GaN island on IS//⟨11¯00⟩sapphire and {11¯01}GaN layer//{0002}GaN island on IS//{12¯13}sapphire was confirmed among the GaN layer, the recrystallized GaN islands on an inclined sapphire surface and the PSS. The flat surface among the protruding patterns began to fill rapidly with GaN. Then, the GaN gradually overgrew the protruding pattern and coalesced near the summit as the growth time increased. The generation of threading dislocations was ob...

During annealing, the morphologies of thin InGaN epilayers have been observed to change from a terraced structure to a network of interlinking InGaN strips separated by troughs. This change in morphology may contribute to high efficiencies in some GaN-based light emitting diodes (LEDs) if the InGaN is exposed to elevated temperatures without a protective GaN capping layer. Here, we investigate the changes in morphology which occur when InGaN epilayers are annealed at their growth temperature under NH3, N2, and a small H2 flux. We observe that while the layers initially roughen, more extended anneals lead to the surface becoming smooth and terraced once again. Power spectral density analysis of atomic force microscopy data is used to show that the dominant mechanism for roughening is loss of material from pre-existing pits, while the dominant smoothening mechanism is surface diffusion. This mechanistic analysis may be relevant to the growth of InGaN quantum wells in LED structures.

Si∕Si1−xGex∕Si heterostructures consisting of relaxed SiGe layers of graded and constant (x=0.2) composition with a strained-Si layer on top have been studied by the capacitance-voltage (C-V), deep-level transient spectroscopy (DLTS), and electron-beam induced current (EBIC) techniques. Analysis of the C-V and EBIC data shows that electrically active defects are introduced during growth into both the graded and constant-composition SiGe layers in a high concentration (∼1016cm−3). The defects are attributed to dislocation trails, i.e., the quasi-two-dimensional extended defects formed behind gliding threading dislocations. Electrical activity of the dislocation trails is reduced following the annealing at 800°C. The DLTS measurements reveal a much lower density of deep-level defects which are mainly located in the graded SiGe layer. The 800°C annealing also gives rise to an additional DLTS peak. The deep-level centers corresponding to this peak are located close to the strained-Si∕SiGe interface and can be...

Short period superlattices of AlN∕Al0.08Ga0.92N with the average AlN content over 60% have been investigated by high resolution x-ray diffraction. The a and c lattice constants verify these structures to be strain relaxed. Monolayer-level interface roughness, caused by the presence of threading dislocations and step-flow growth mode, is simulated and directly compared with the zeroth and ±1 satellite peak positions of the rocking curves. It was found that the observed x-ray diffraction data can be adequately described by considering primarily the presence of screw dislocations and step-flow growth mode.

A variety of different transmission electron microscopy techniques, and particularly high-angle annular dark-field scanning transmission electron microscopy, has been used to reveal that V defects or inverted hexagonal pyramid defects in multiple InGaN∕GaN quantum well (QW) layers nucleate on threading dislocations that cross the InGaN QW. The defects have thin walls lying parallel to {101¯1} with the InGaN∕GaN QW structure. A formation mechanism for the V defects is proposed taking into account the growth kinetics of GaN and the segregation of In atoms in the strain field around the cores of the threading dislocations.

We investigate the temperature dependence of Hall mobility μ and carrier density Ne for thin InN films grown by molecular-beam epitaxy and plasma source molecular-beam epitaxy over three orders-of-magnitude difference in their carrier density: for the low-density film Ne=5.8×1017∕cm3 and for the high-density film Ne=3.2×1020∕cm3. In both the films, for temperature up to 300 K, a large temperature-independent concentration of carriers is observed. For higher temperatures, however, carrier density increases with temperature. The characteristic behavior of the mobility for the low-density film is different from that of the high-density film, particularly for temperatures less than 300 K. The low-density film shows a peak behavior in the mobility around 250 K in contrast to the temperature-independent mobility observed for the high-density film for T

A method for measuring the mean free path of laterally gliding threading dislocations, based on the growth of lattice mismatched epitaxial layers on patterned substrates has been presented. The method requires no post growth annealing and permits an accurate measurement of the glide process as it occurs during epitaxial growth. This method has been applied to an InGaAs/GaAs heterostructure with a lattice mismatch of 0.5%. Mean free paths of 960 μm for α type dislocations and 1000 μm for β type dislocations were measured. It was concluded that the interaction of threading dislocations with clusters of misfit dislocations and/or edge type dislocations was the primary mechanism of glide length attenuation.

In heavily dislocated material (dislocation density of mid‐107 cm−2), the low‐temperature cathodoluminescence intensity of a sufficiently short‐period superlattice comes remarkably close to that of comparison structures grown on low‐dislocation material. We attribute this effect to a redistribution of the recombination‐active sites along the dislocation cores taking place in the material. The driving force of such redistribution may be electrical or chemical in nature.

InGaAs‐GaAsP strained‐layered superlattices have been used as a buffer layer to reduce the dislocation density in GaAs grown on Si substrates. These superlattices have been grown lattice matched to GaAs. Several interactions between the strain field of the strained layered superlattice [GaAs1−yPy‐InxGa1−xAs (y=2x)] and the threading dislocations in GaAs/Si are observed. Mixed dislocations are strongly affected by the strain field of the superlattice, however, the interactions with the edge dislocations are less likely to occur. The stress field associated with the strained layered superlattice has a shear component that forces the 60° mixed dislocations to bend at the strained layered superlattice interfaces. Dislocations annihilation or repulsion are observed at the superlattice interfaces.