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We investigated the electrical properties of low-threading-dislocation-density (TDD) GaN crystals grown by Thin-Flux-Growth method in the Na-flux point seed technique for the first time. In addition, we attempted to fabricate GaN crystals with further lower TDD and curvature by using point seeds having a smaller diameter of 250 µm, compared to that from the previous study having a diameter of 1000 µm. As a result, free carrier concentration was 1.1×10^20 cm^(-3) with a resistivity of 9×10^(-4) Ωcm. Moreover, TDD in about 80% of the observation area was on the order of 10^3 cm^(-2) or less, and the radius of curvature of the GaN crystal was over 100 m for both a// and m//, due to the smaller-sized point seeds. These results suggest that low-TDD GaN crystals with low resistivity can be realized with this method, and Na-flux-GaN crystals exhibit a great performance as substrates of power devices.

The increase in threading dislocation during the initial stage of physical vapor transport growth of n-type 4H-SiC crystals was evaluated by cross-sectional X-ray topography. Crystals were grown under two different temperature conditions. A significant increase in threading dislocation was observed in crystals grown at a high, not low, temperature. The local strain distribution in the vicinity of the grown/seed crystal interface was evaluated using the electron backscatter diffraction technique. The local nitrogen concentration distribution was also evaluated by time-of-flight secondary ion mass spectrometry. We discuss the relationship between the increase in threading dislocation and the local strain due to thermal stress and nitrogen concentration.

Recently, gallium nitride (GaN) films grown on graphene have been widely studied. Here, we have grown low-threading-dislocation-density GaN films on graphene by hydride vapor phase epitaxy (HVPE). The full widths at half maximum (FWHMs) of X-ray rocking curves (XRCs) of the GaN films were 276 and 350 arcsec at the 0002 and reflections, respectively. This shows that the threading dislocation densities are on the order of magnitude of 108 cm−2, which is consistent with the results of cathodoluminescence (CL).

Threading dislocations (TDs) are inclined from the [0001] c-axis in 4H-SiC epilayers which are produced by the step-controlled technique. The reason for this inclination is discussed in the framework of isotropic elastic theory of dislocation. The elastic strain energy of a TD in an epilayer is calculated as a function of its orientation, and the minimum energy orientation is used to predict the inclination angle. The results of the calculations are as follows. For a cut-off angle (α) of 4°, a threading edge dislocation (TED) and a threading pure screw dislocation (TpSD) are inclined from the c-axis by 12 and 2°, respectively: Threading near screw dislocations (TnSDs) and threading mixed dislocations (TMDs) are inclined by angles ranging from 8 to 15° from the c-axis, depending on their actual Burgers vectors. Similarly for α of 8°, a TED and a TpSD are inclined from the c-axis by 21 and 4°, respectively: TnSDs and TMDs are inclined from the c-axis by angles ranging from 7 to 17°. These predictions are in good agreement with experiment.

The edge dislocation in GaN has been investigated by means of atomistic computer simulation. It's core structure exhibits three configurations that are related to the location of the origin of displacements imposed to the atoms when generating the dislocation in the initial configuration. They are described by: (a) 8- and 4-coordinated channels (8/4 core); (b) 8-, 5-, and 5-coordinated channels (8/5/5 core); and (c) 9- and 5-coordinated channels (9/5 core). An additional configuration where the dislocation decomposes in two 8-coordinated channels a= 1/3 dislocations is also generated and it exhibits the lowest energy. This is in agreement with high resolution transmission electron microscopy observations and image simulations carried out on an asymmetric Σ7 [0001] tilt grain boundary in which only cores of elemental a type dislocations have been determined.

Using the epitaxial lateral growth technique, we compared the crystallinity and relaxation ratio of 3-µm- and 200-nm-thick Al0.5Ga0.5N on an AlN template and AlN grown by epitaxial lateral overgrowth (ELO-AlN), both of which were grown on a sapphire substrate. Although the relaxation ratios of 3-µm-thick Al0.5Ga0.5N were almost the same, the misfit dislocation density at the interface and the density of threading dislocations reaching the surface of Al0.5Ga0.5N were significantly different. Also, the increase in the density of newly generated misfit dislocations was found to be highly dependent on the quality of the AlN underlying layer. We also discuss the difference in the initial growth mode of each Al0.5Ga0.5N sample.

We performed a plan-view and cross-sectional photoluminescence (PL) imaging and a spectral analysis of threading dislocations in 4H-SiC epilayers in the near-infrared region. The bright PL spots of threading screw dislocations (TSDs) and threading edge dislocations (TEDs) observed in the plan-view PL imaging are compared with the grazing incidence synchrotron X-ray topography contrast, and precise discrimination of threading dislocations using the PL technique and the direct acquisition of Burgers vector directions of TEDs are demonstrated. The inclination angles of TSDs and TEDs across a thick epilayer are revealed by the cross-sectional PL imaging, and the variations in the plan-view PL appearances of the threading dislocations are confirmed to originate from the line directions of such dislocations.

In this work, the threading dislocation suppression effects of InAs/In0.52Al0.48As digital alloy intermediate layers in an InP-based InAlAs graded metamorphic buffer were investigated to improve the structural and optical qualities of the buffer. Cross-sectional transmission electron microscopy, atomic force microscopy, and photoluminescence measurements proved that the insertion of thin digital alloy layers in the graded buffer markedly improves the surface quality, decreases the threading dislocation density, and enhances the photoluminescence efficiency of In0.8Ga0.2As/In0.8Al0.2As quantum wells. This study shows great potentials by incorporating digital alloy intermediate layers in metamorphic buffers to improve the quality of metamorphic devices.

The dislocation structure that forms the caterpillar-shaped etch pit upon molten KOH etching is investigated by transmission electron microscopy employing a weak-beam dark-field method. The observed dislocation has the Burgers vector 1/3[1̄21̄0], and its structure was transformed from a basal plane dislocation to a threading edge dislocation. In the basal plane dislocation region, it propagated parallel to the [101̄0] direction. On the basis of the measured dislocation structure, the caterpillar pit formation is explained. The process of dislocation formation is discussed by analyzing the relationship between sample types and the detection of the caterpillar pits.

Dislocations in 4H-SiC epilayers were imaged nondestructively by means of micro photoluminescence (µ-PL) mapping at room temperature. The one-to-one correspondence between the individual dislocations and the µ-PL mapping contrast has been consistently obtained. By analyzing the reduction of the intensity in the µ-PL mapping image performed at 390 nm (near band-edge emission), we were able to distinguish threading screw dislocations and threading edge dislocations. Furthermore, it was found that a basal plane dislocation dissociates into a single Shockley stacking fault during the measurement.

Two types of AlN defect structures directly grown on sapphire (0001) by metalorganic vapor-phase epitaxy with different initial growth sequences were studied. One was a domain structure with arrays of threading edge dislocations aligned along the [1-210] direction, observed in AlN with NH3 preflow. The other was threading dislocations with screw components located randomly, observed in AlN with TMA preflow. It was also confirmed that threading dislocations caused the surface depression of AlN. A model for the formation of domain structures based on the geometrical aspects and dislocation types is proposed.

We have investigated the reduction of threading dislocations and the suppression of crack formation in In x Ga1-x P (x∼ 0.5) grown on Si using the multi-strained short-period superlattices (SSPSs) by transmission electron microscopy (TEM). The epitaxial layers were grown two-dimensionally and the density of threading dislocations was reduced by the generation of misfit dislocations at all hetero-interfaces. The residual strain was reduced by compensation of the lattice-mismatched stress and the thermal stress, and the formation of cracks was suppressed by controlling the In composition.

This paper examines the reduction of threading dislocation by a thin strained interlayer (SIL), and a long-wavelength laser fabricated on a GaAs substrate with SILs. A cross-sectional transmission electron microscope is used to observe the dislocation blocking ability of an SIL made of InGaP, which is inserted in an InP layer grown on a GaAs substrate. The characteristics of the BH laser emitting at 1.3 µm on GaAs are investigated. Most of them are improved by SIL insertion. In particular, threshold current is reduced to 70% on average and is also distributed more uniformly.

This paper reports on a new approach for reducing the threading dislocation density in GaAs on Si. We have used In x Ga1-x As/GaAs strained-layer superlattices (SLSs) grown on GaAs/Si at 300°C by migration-enhanced epitaxy as threading dislocation barriers. Different from conventional high-temperature-grown SLSs, the low-temperature-grown SLSs are only slightly relaxed by misfit dislocation formation at GaAs/SLS interfaces. Thus, considerable strain can be accumulated in SLS. In addition, new threading dislocation generation due to the misfit dislocation can be suppressed. These factors lead to effective threading dislocation bending and to significant reduction in the dislocation density. For the samples with a SLS of x=0.3, the average etch-pit density is 7×104 cm-2, which is the lowest value ever reported.