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We have investigated the morphology of the high-temperature-grown AlN nucleation layer and its role in the early stage of GaN growth, by means of transmission electron microscopy. The nitride was selectively grown on a 7-degree off-oriented (0 0 1) patterned Si substrate by metalorganic vapor phase epitaxy. AlN was deposited on the inclined unmasked (1 1 1) facet in the form of islands. The size of the islands varied along the slope, which is attributable to the diffusion of the growth species in the vapor phase. The GaN nucleation occurred at the region where rounded AlN islands formed densely. The threading dislocations were observed to generate in the GaN nucleated region. [Copyright &y& Elsevier]

The selective growth of wurtzite GaN was performed by MOVPE on (1 1 1) facets on a patterned 7-degree off-oriented (0 0 1) silicon substrate, which had been prepared by anisotropic etching with KOH solution. The c-axis of the GaN was along the 〈1 1 1〉 axis of the silicon. At an early growth stage, the shape of the crystal grown selectively was a stripe having truncated triangular cross-section and its (1 1¯ 0 1) facet was parallel to the substrate surface. After a sufficient growth duration, the stripes coalesced with each other and a GaN film with a flat (1 1¯ 0 1) surface was achieved. [Copyright &y& Elsevier]

The selective growth of wurtzite GaN was performed on a (1 1 1)silicon substrate by metalorganic vapor phase epitaxy. By limiting the size of GaN to the area of 0.5 mm×0.5 mm, a single GaN crystal without cracks was obtained. As a result, the full-width at half-maximum of the (0 0 0 4) X-ray-rocking curve as well as that of the band edge emission were much reduced as compared to the samples grown by a conventional method. [Copyright &y& Elsevier]

Growth of GaN/AlGaN heterostructure and quantum well (QW) on the (1 &1macr;0 1) side facets of truncated triangular GaN which is grown on a (1 1 1) silicon substrate is demonstrated for the first time. The cathode luminescence image showed that the composition of AlGaN is not uniform on the side facets, but the photoluminescence spectra exhibited clear peaks, which were attributed to the GaN QW embedded between AlGaN cladding layers. [Copyright &y& Elsevier]

Thermal annealing at high temperatures of nonpolar (1 0 1 ¯ 0) m -plane AlN layers directly sputtered on m -plane sapphire was investigated. The crystallinity of the layers increased with increasing annealing temperature. The full-width at half maximum of the symmetric (1 0 1 ¯ 0) X-ray rocking curves along [0 0 0 1]/[1 1 2 ¯ 0 ] AlN decreased from about 3.5/2.0 ° to 0.24/0.19 ° . The density of basal stacking faults of the annealed layers was found to decrease from ∼ 1 × 10 5 to ∼ 5 × 10 3  cm −1 . The annealed layers had a larger optical bandgap energy than the as-sputtered layers due to their better crystallinity and structural order. [ABSTRACT FROM AUTHOR]

Abstract: A novel activation process for Mg-implanted GaN was demonstrated. As opposed to the conventional thermal annealing process, an H2/NH3 alternating supply annealing process achieved better optical activation, stronger near-ultraviolet luminescence and weaker yellow luminescence in the photoluminescence spectroscopy. After this process, small hexagonal hillocks were observed on the surface, which indicated that crystal regrowth was induced by this process, consisting of decomposition of GaN by H2 supplies and re-crystallization by NH3 supplies. It was revealed that the implanted Mg could easily be located at the activation site by means of crystal regrowth by this process. [Copyright &y& Elsevier]

Abstract: Mg doping was attempted in (11¯01)GaN grown on a patterned (001)Si by selective metal-organic vapor phase epitaxy (MOVPE). The source material for the Mg doping was EtCp2Mg and the electrical properties were studied on samples with different doping levels. All samples showed p-type conduction. However, the hole concentration was decreased by the Mg doping at low doping levels followed by an increase at high doping levels. The activation energy was around 106–130meV depending on the doping level, which was larger than that found in undoped or carbon-doped samples. The AFM images showed gradual change in the surface structure in accordance with the Mg-doping level. The variation of the optical spectra was discussed in relation to the Mg-doping levels. [Copyright &y& Elsevier]

• Sn-doped n-type GaN layers were grown by halide vapor phase epitaxy. • Sn precursor was formed by reacting Sn metal with HCl gas. • Sn concentration in GaN layers increased with decreasing the growth temperature. • High electron density of 2 × 1020 cm−3 was achieved. • Sn introduction promoted the surface migration of Ga adatoms. A Sn-doped n-type GaN layer with a high electron density of 2 × 1020 cm−3 and a low resistivity of 8.7 × 10−4 Ω∙cm was grown by halide vapor phase epitaxy (HVPE). Sn doping was performed through the reaction between Sn metal and HCl gas. The Sn concentration markedly increased with decreasing growth temperature and the activation energy of Sn desorption from the GaN surface was found to be 4.1 eV. Smooth surfaces were obtained by introducing the Sn precursor even though the samples were grown at a low temperature of 905 °C, suggesting that Sn atoms act as surfactants and promote the migration of Ga adatoms. Almost all the Sn atoms act as donors in GaN below the Sn concentration of 2 × 1020 cm−3. These results indicate that using the Sn donor is promising for fabricating low-resistivity n-type GaN substrates by HVPE. [ABSTRACT FROM AUTHOR]

Highlights • Low impurities concentration in GaN grown by MOVPE using quartz free reactor. • N-polar GaN atomic steps with double height. • Different off-cut angle N-polar GaN for homo-epitaxial growth. Abstract This study examines the effect of (0 0 0 −1) GaN substrate misorientation on the residual impurities and surface morphology of N-polar GaN grown by metalorganic vapor-phase epitaxy. Carbon, silicon, and oxygen concentrations decreased with increasing GaN substrate misorientation angle, with the lowest impurity concentration achieved for a misorientation angle of 2° toward the m-axis, with 6 × 1015 cm−3 carbon, 6 × 1015 cm−3 silicon, and 4 × 1017 cm−3 oxygen atoms. The oxygen concentration was measured at a depth of 0.5 μm below the wafer surface, and the oxygen concentration decreased with increasing thickness. The incorporation of carbon and oxygen revealed a strong dependence on the misorientation angle. The step distance height of the steps parallel to the [1 1 −2 0] direction (or perpendicular to the [1 −1 0 0] m-direction) was confirmed to be a double-height layer step. This phenomenon indicated that m-direction steps are stable for N-polar growth in GaN. In cases of large misorientation toward the m-axis in of the GaN substrate it was difficult to control the misorientation perpendicular to the nominal direction leading to a-axis direction by wafer bowing at wafer manufacturing. Therefore, step-bunching was generated for each symmetric m-axis due to an increase in the compound's off-angle, thus causing the surface roughness to become large. [ABSTRACT FROM AUTHOR]

Hexagonal boron nitride (h-BN) was directly grown on sapphire substrate using alternating ammonia (NH 3 ) and triethylboron (TEB) supply (pulsed mode) in metalorganic vapor phase epitaxy. The best condition is when just enough NH 3 is supplied to fully convert the TEB within one cycle. Excess NH 3 caused islands on h-BN film surface while a lack of NH 3 does not form h-BN at all. The epitaxial relationship between grown h-BN layer and c -plane sapphire was confirmed to be [0001] h-BN ∥[0001] sapphire and [10-10] h-BN ∥[11-20] sapphire . It is known that, compared to AlN, BN requires higher V/III ratios for good crystallinity, which due to severe gas-phase reactions is difficult to achieve using continuous supply. Thus using pulsed mode the FWHM of the symmetric (0002) diffraction was almost halved and the growth rate was several times faster. [ABSTRACT FROM AUTHOR]

A-plane GaN was attempted to be grown on (11-20) 4H-SiC bulk substrate without using a traditional thick buffer layer. By inducing TMAl treatment before the GaN growth step and using both a low pressure and V/III ratio, the interlayer thickness of the a-plane GaN/SiC was reduced to 1.7 + 0.5 nm. The ultrathin interlayer was observed to be either AlN or AlGaN with a low Ga composition. This study is aimed to contribute to the understanding of GaN growth on the sidewalls of c-plane trench structure SiC. The ultrathin growth technique is also hoped to be applied to the fabrication of GaN-based vertical structure nonpolar optical or electrical devices. [ABSTRACT FROM AUTHOR]

• A surface kinetic model of HVPE-GaN (0001) layers is developed using BCF theory. • The hillock density is controlled by the supersaturation and/or the off-cut angle. • The critical off-cut angle is controlled by the supersaturation. The effects of halide vapor phase epitaxial (HVPE) growth conditions such as input V/III ratio and substrate off-cut angle on the surface morphology of n-type GaN layers grown on GaN (0001) freestanding substrates were investigated to develop a model for growing smooth surfaces. The spiral hillock density increased with increasing input V/III ratio and/or decreasing off-cut angle. The critical off-cut angle between the spiral growth and the step-flow growth depended on the vapor supersaturation calculated by thermodynamic analysis. To understand the transition of the growth mode, we proposed a Burton–Cabrera–Frank-theory-based model considering the effect of spiral growth, which was utilized to explain the obtained experimental results. The developed growth model can be effective for predicting the HVPE growth mode between the spiral growth and the step-flow growth. [ABSTRACT FROM AUTHOR]

Abstract: Semi-polar (112¯2) GaN layers were selectively grown by metal organic chemical vapor phase epitaxy on patterned Si (311) substrates without SiO2 amorphous mask. The (112¯2) GaN layers could be selectively grown only on Si (111) facets when the stripe mask width was narrower than 1μm even without SiO2. Inhomogeneous spatial distribution of donor bound exciton (DBE) peak in low-temperature cathodoluminescence (CL) spectra was explained by the difference of growth mode before and after the coalescence of stripes. It was found that the emission intensity related crystal defects is drastically decreased in case of selective growth without SiO2 masks as compared to that obtained with SiO2 masks. [Copyright &y& Elsevier]

Abstract: Adopting anisotropy etching method, a (111) facet of Si is obtained on a Si substrate and selective area growth (SAG) of GaN is performed with metal-organic vapor phase epitaxy on the facet. The epitaxial lateral overgrowth of (11¯01), (112¯2) GaN is investigated on (001) and (113) Si substrate, respectively, and the incorporation properties of Si, C, and Mg elements are discussed in relation to the atomic configuration on the surface. Analyzing the optical and electrical properties of C-doped (11¯01) GaN layer, it is shown that carbon creates a shallow acceptor level. On the thus prepared (11¯01) GaN layer, a light emitting diode (LED) with a C-doped p-type layer is fabricated. [Copyright &y& Elsevier]

• P-type GaN layers with Mg concentrations of 8.0 × 1018–8.3 × 1019 cm−3 are fabricated by HVPE. • The electrical properties and structural defects of p-type GaN layers are characterized. • Pyramidal inversion domains are observed in the heavily Mg-doped GaN layers grown by HVPE. • Mg atoms accumulate in pyramidal inversion domain. The electrical properties and structural defects of p-type GaN layers with Mg concentrations from 8.0 × 1018 to 8.3 × 1019 cm−3 grown by halide vapor phase epitaxy (HVPE) were investigated. In all samples, p-type conduction was confirmed at room temperature. The hole concentration at room temperature decreased in a heavily Mg-doped sample. By analyzing the results of Hall-effect measurements at various temperatures, the acceptor concentration decreased in a heavily Mg-doped sample, whereas the compensating donor concentration increased. These results affect the decrease in the hole concentration. The hole mobility decreased with increasing acceptor concentration. In the heavily Mg-doped sample, pyramidal inversion domains (PIDs) were formed. The size of each PID in an HVPE-grown sample is in good agreement with that Mg-doped GaN layers grown by metalorganic vapor phase epitaxy (MOVPE). Thus, the formation mechanism of PIDs in HVPE-grown samples is possibly the same as that in MOVPE-grown samples. Energy-dispersive X-ray spectroscopy shows that Mg atoms accumulate in PIDs, which suggests that Mg atoms in PIDs are electrically inactive, inhibiting the increase in the acceptor concentration. These results are useful guidelines for fabricating p-type GaN layers with higher hole concentrations by HVPE. [ABSTRACT FROM AUTHOR]

• Lattice bow generated by HVPE layers on free-standing GaN wafers was studied. • Samples include HVPE homoepitaxial layers on ammonothermal and HVPE GaN wafers. • Bow increased on all samples but on the ammonothermal GaN wafers was minimal. • Lattice bow increase was related to elongation of dislocations via climb. Lattice bow generated by 40 µm thick HVPE homoepitaxial layers on commercial free-standing, ammonothermal and HVPE GaN wafers was studied. While a change in lattice bow was measured for all wafers, the additional bow on the ammonothermal GaN wafers was minimal. The main driving force for the observed increase in the lattice bow for HVPE wafers was related to stress in the films generated by the elongation of dislocations via climb and generation of new dislocations at the homoepitaxial interface. Lattice bow is a crucial wafer parameter as it determines the variation of the offcut across the surface. If an offcut variation of 0.1° is allowed for desired control surface morphology, composition of alloys, and uniformity of doping on this surface, the measured bow on the two HVPE GaN wafers and one ammonothermal GaN wafer limits their uniformity-diameter to ~0.5″, 1″ and >4″, respectively. [ABSTRACT FROM AUTHOR]