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• A β-Ga 2 O 3 crystal with a diameter of 30 mm was grown by the LDFZ method. • The beam profile was adjusted to heat the molten zone locally and intensively. • Three beam profile patterns were switched with increasing the crystal diameter. • Proper beam profile and proper diameter of the feed rod keep the molten zone stable. To investigate the effect of high-power laser heating on the floating zone (FZ) method, a crystal of β-Ga 2 O 3 was grown by the LDFZ method using a newly developed optical system equipped with a 20-kW laser diode (LD) system as a heat source. The growth started from a twin-free seed crystal with a diameter of 7 mm and the diameter of the crystal was increased gradually up to 30 mm. With increasing the diameter of the crystal, three patterns of the beam intensity profile were switched to heat the whole of the molten zone locally and intensively. The intensity profile of the five beamlets irradiating the sample was adjusted with a combination of the zooming by the optical system and the partial blocking by the alumina cylinder. By the proper tuning of the beam profile and the proper selection of the diameter of the feed rod, the molten zone was kept stable against gravity. The obtained crystal has a layer texture without clear facets or cracks. It almost conserves the crystallographic direction of the seed crystal but is twinned except for a twin-free region near the seed crystal. [ABSTRACT FROM AUTHOR]

• Capability to monitor growth rate of III-Nitrides, by MBE, at any point during the growth of the film or device structure. • Innovative differential analysis method which increases accuracy (reduces error) by more than 2x over previous methods. • Measurement of the Ga adlayer thickness made by RHEED Intensity analysis for the first time. The standard method for growth rate determination in semiconductor thin films, by Molecular Beam Epitaxy (MBE), is through RHEED intensity oscillations prior to device layer epitaxy. High quality III-Nitride epitaxy occurs with metal-rich surfaces and under step-flow growth conditions, which do not produce RHEED oscillations. This article demonstrates the capability to monitor the growth rate of gallium nitride (GaN), at any point during film growth with high fidelity, under step-flow growth conditions. RHEED intensity vs. time measurements determine the growth rate by Metal Modulated Epitaxy (MME). Utilizing differential analysis, a factor of 2x improvement in accuracy is demonstrated, with a Standard Error less than 4%. Complementary analysis with X-Ray Diffraction and RHEED identify the Ga bilayer thickness as 2.34 ML ± 0.08 ML, representing the first time RHEED analysis has been used to characterize the thickness of the Ga bilayer on GaN. [ABSTRACT FROM AUTHOR]

Highlights • Slight variations in ultrathin AlN prelayers result in drastic GaN NW changes. • Increasing the AlN nominal thickness between 0 and 0.5 nm, doubles NW heights. • Simultaneous increase in NW height and decrease in diameter and density is found. Abstract The effects of ultrathin AlN prelayers, with nominal thicknesses between 0 and 1.5 nm, on the spontaneous growth of GaN nanowires (NWs) on Si (1 1 1) substrates were investigated. The morphological and structural characteristics of GaN NWs were analyzed by electron microscopy and X-ray diffraction techniques. The results quantify how the AlN prelayer thickness affects GaN NWs. The increase of AlN thickness gradually limits nitridation of the substrate surface and accelerates 3D GaN nucleation. The formation of amorphous Si x N y by Si nitridation is completely avoided for 1.5 nm of AlN that fully covers the Si surface. The dependence of the height, diameter and density of GaN NWs on the AlN thickness was also determined. The 1.5 nm AlN provided the optimum condition for GaN NW nucleation and growth; the NWs exhibited a large homogeneous height with almost no parasitic GaN formation between them. High resolution transmission electron microscopy showed the full relaxation of misfit strain of AlN on Si (1 1 1) and of GaN NWs on AlN. In-situ reflection high energy electron diffraction during AlN nucleation revealed the immediate relaxation of the AlN prelayer before GaN NW nucleation. Formation of β-Si 3 N 4 before AlN nucleation was also observed. [ABSTRACT FROM AUTHOR]

Highlights • Electron mobility of 2DEG on AlGaN/GaN was degraded by regrown interface. • Regrown interface of GaN had Si impurities and unintentional carrier. • Contamination of GaN surface by Si compounds was caused to exposure of air. • Cleaning of regrown interface improve device properties of AlGaN/GaN FET. Abstract In this paper, the influence of a regrown interface on the electrical properties of AlGaN/GaN heterostructure was investigated for recessed-gate MOSFETs fabricated by selective area regrowth. The electron mobility of the two-dimensional electron gas (2DEG) on regrown AlGaN/GaN structures was degraded when the 2DEG was near the regrown interface. The regrown interface had high carrier concentrations and Si impurities that caused degradation of the electron mobility of the 2DEG. Unintentional carrier generation at the regrown interface was eliminated by ultraviolet (UV) treatment before regrowth. A regrown AlGaN/GaN MOSFET device was then fabricated using the UV treatment. The device exhibited good performance such as normally-off operation without hysteresis or leaks. Improvement of the electrical characteristics of AlGaN/GaN MOSFETs was thus achieved by suppression of regrown interface charge. [ABSTRACT FROM AUTHOR]

Highlights • The high density and large quantity β-Ga 2 O 3 microbelts were synthesized on PSS by CVD method. • The width and length of microbelts were about 1–1.5 μm and 15 μm, respectively. • The hemispherical PSS played an important role for β-Ga 2 O 3 microbelts formation. Abstract The high density and large quantity β-Ga 2 O 3 microbelts were synthesized by changing the growth temperature on patterned sapphire substrates (PSS) by chemical vapor deposition equipment. The width of the microbelts was about 1–1.5 μm, and the length was about 15 μm. The results of different growth temperature influenced for surface morphology and crystal structure of β-Ga 2 O 3 indicated that the optimal growth temperature of β-Ga 2 O 3 microbelts was at 900 °C. Furthermore, the growth mechanism of microbelts was also studied. It was found that the hemispherical PSS played an important role for β-Ga 2 O 3 microbelts formation. The optical absorption spectrum indicated that optical band gap energy of microbelts was about 4.78 eV. [ABSTRACT FROM AUTHOR]

Highlights • Laser molecular beam epitaxy growth of GaN nanorods on flexible Ti metal foil. • Tuning of shape and size of GaN nanostructures with growth temperature. • Growth of sparse GaN nanorods on Ti foil at 700 °C growth temperature. • High structural and optical quality of GaN nanorods directly grown on Ti foil. Abstract We have studied the effect of growth temperature (550–700 °C) on the morphological, structural and optical properties of GaN nanostructures grown directly on flexible Ti metal foil by laser assisted molecular beam epitaxy (LMBE). The low growth temperature (550 °C) favors a growth of dense, three-dimensional GaN islands whereas probe-shaped sparse GaN nanorods (NRs) are obtained at 700 °C. The average length, diameter and density of GaN NRs were analyzed from field emission scanning electron microscopy images and were estimated to be 80 nm, 260 nm and ∼9.6 × 108 cm−2 respectively. The high-resolution transmission electron microscopy analysis confirmed that the GaN NRs have single crystalline structure over the entire length and had grown along c-axis. Raman spectroscopy studies revealed that the LMBE grown GaN nanostructures on Ti foil possess wurtzite structure with a low tensile stress (0.15–0.37 GPa). The intense near band edge emission peak appeared at 3.42 eV, similar to bulk GaN, with a smaller full width at half maximum of 100 meV for the sparse GaN NRs grown at 700 °C. Direct growth of GaN NRs at a relatively lower temperature on flexible metal foils with high structural and optical quality holds the promise for the fabrication of flexible GaN based futuristic optoelectronics devices. [ABSTRACT FROM AUTHOR]

Highlight • The properties of β-Ga 2 O 3 are studied based on first-principles calculations. • The pressures on β-Ga 2 O 3 are ranged from 0–30 GPa. • The elastic constants of β-Ga 2 O 3 are satisfied with the mechanical criteria. • The bandgap for β-Ga 2 O 3 increase monotonously with the pressures. Abstract The structural, anisotropic elastic and electronic properties of β-Ga 2 O 3 under pressures ranged from 0 to 30 GPa are studied based on first-principles calculations. The results indicate that β-Ga 2 O 3 is more compressible under high pressures. The elastic constants of β-Ga 2 O 3 are satisfied the mechanical criteria in the most pressure range expect for 30 GPa. The mechanical moduli have been calculated, and the anisotropy in Young's modulus of β-Ga 2 O 3 is discussed by plotting both the 3D contours and the 2D planar projections of their Young's modulus. It is shown that the Young's modulus of β-Ga 2 O 3 strongly depend on directions. The bandgap of β-Ga 2 O 3 as a function of pressure is calculated, which indicate that the bandgap for β-Ga 2 O 3 increase monotonously with the pressures. [ABSTRACT FROM AUTHOR]

Highlights • Carbon deposition on sapphire by propane pyrolysis in III-N MOVPE reactor is studied. • Conditions, resulting in graphene layers formation are optimized. • Graphene stability in various reactor conditions is studied. • III-N structures growth on graphene in a single epitaxial process is developed. • Large-area defoliation of the formed III-N structures is demonstrated. Abstract We investigated the growth of III-N/graphene heterostructures as a single process in a MOVPE reactor. Raman spectra revealed that graphene can be successfully deposited on sapphire substrate by propane pyrolysis if temperature exceeds 1060 °C and hydrogen is used as a carrier gas. GaN epitaxial layers and heterostructures on such graphene using both high-temperature AlN buffer layer and low-temperature GaN nucleation layer was demonstrated. Analysis of surface morphology and X-Ray diffraction curves indicate that GaN quality depends on graphene thickness. Use of copper electroplated Ni-based contact layer combined with thermal shock allows exfoliation of large-area III-N LED structures from sapphire. [ABSTRACT FROM AUTHOR]

Highlights • 2 in. GaN crystals and wafers were produced by ammonothermal method. • X-ray characterization method suggested to check surface and subsurface damage. • (1 1 4) X-ray rocking curves measurements for each step of back-end processing. • Lack of uniformity of surface damage from different companies and from sample to sample. Abstract SixPoint Materials has successfully switched to production of two-inch diameter GaN wafers using the ammonothermal method. Crystal quality values are high with dislocation densities typically in the low 105 cm−2. In efforts to produce true epi-ready material, investigations were made to develop a technique to study surface damage caused by the back-end process using X-ray diffraction methods. Analysis of peak tailing from X-ray rocking curves of the (1 1 4) reflection indicates the progression of surface damage during each step of the back-end process. For instance, the tailing can be partially represented using full width five thousand max (FW5000M) values. By using a peak with a low glancing angle, such as the (1 1 4) reflection's angle of 10.8662°, more of the X-ray beam is scattered in the surface region, providing an improved measurement of surface damage. Since this technique is non-destructive and can be performed without dismounting the sample from its ceramic back-end processing plate, it can provide information on the damaged layer at each stage of the back-end process. Using this technique to evaluate samples from various manufacturers, we found a lack of uniformity in surface damage from GaN companies. It is our hope that this technique will be adopted to better standardize surface damage measurements in the GaN field. [ABSTRACT FROM AUTHOR]

Powder and polycrystals synthesized from Ga, Se, Er components, as well as GaSe and GaSe:Er single crystals grown from melt in argon atmosphere and in vacuum, respectively, are studied. The growth and quenching conditions used in this work provide 2.5 times increase in solubility of erbium in GaSe matrix and a decrease in number of phases to GaSe and Er 2 Se 3 , oppositely to multiphase GaSe:Er alloys known from literature. For the first time Er 2 Se 3 phase was detected by XRD in GaSe crystal doped with 1 at%Er. Possible orientation relations are derived for Er 2 Se 3 /GaSe epitaxial pair. It has been shown that stretched reflections in electron micro diffraction patterns and scattering of maximums in x-ray diffraction patterns are bound to stacking faults, which appear owing to thin interlayers of δ-GaSe polytype in ε-GaSe matrix of the melt-grown crystals. Morphology of growing crystal surface is studied. Photoluminescence spectra of pure and erbium-doped GaSe display intense photoluminescence bands, which are, presumably, associated with defect states in band gap of GaSe. It is shown that doping with Er has a strong effect on photoluminescence intensity and on its spectral composition. The measured 1.7 times increase in Vickers microhardness (up to 400 MPa) with respect to pure GaSe is due to solid solution hardening and to precipitation. [ABSTRACT FROM AUTHOR]

α-Ga 2 O 3 is a metastable phase of Ga 2 O 3 of interest for wide bandgap engineering since it is isostructural with α-In 2 O 3 and α-Al 2 O 3 . α-Ga 2 O 3 is generally synthesised under high pressure (several GPa) or relatively high temperature (∼500 °C). In this study, we report the growth of α-Ga 2 O 3 by low temperature atomic layer deposition (ALD) on sapphire substrate. The film was grown at a rate of 0.48 Å/cycle, and predominantly consists of α-Ga 2 O 3 in the form of ( 0001 ) -oriented columns originating from the interface with the substrate. Some inclusions were also present, typically at the tips of the α phase columns and most likely comprising ε-Ga 2 O 3 . The remainder of the Ga 2 O 3 film – i.e. nearer the surface and between the α-Ga 2 O 3 columns, was amorphous. The film was found to be highly resistive, as is expected for undoped material. This study demonstrates that α-Ga 2 O 3 films can be grown by low temperature ALD and suggests the possibility of a new range of ultraviolet optoelectronic and power devices grown by ALD. The study also shows that scanning electron diffraction is a powerful technique to identify the different polymorphs of Ga 2 O 3 present in multiphase samples. [ABSTRACT FROM AUTHOR]

The crystal orientation relationship between β-Ga 2 O 3 and MgO in β-Ga 2 O 3 thin films prepared on (1 0 0), (1 1 1), and (1 1 0) MgO substrates was investigated by X-ray diffraction measurements and cross-sectional transmission electron microscopy images. The γ-Ga 2 O 3 interfacial layer was present between β-Ga 2 O 3 and MgO acted as a buffer to connect β-Ga 2 O 3 on MgO. The following conditions were satisfied under each case: β-Ga 2 O 3 (1 0 0)||MgO (1 0 0) and β-Ga 2 O 3 [0 0 1]||MgO 〈0 1 1〉 for the formation of β-Ga 2 O 3 on (1 0 0) MgO, and β-Ga 2 O 3 ( 2 ¯ 0 1 )||MgO (1 1 1) for the formation of β-Ga 2 O 3 on (1 1 1) MgO, as well as each condition of β-Ga 2 O 3 [0 1 0] (1 0 0)||MgO [ 1 ¯ 1 0 ] (0 0 1), β-Ga 2 O 3 [0 1 0] (1 0 0)||MgO [ 0 1 ¯ 1 ] (1 0 0), and β-Ga 2 O 3 [0 1 0] (1 0 0)||MgO [ 1 0 1 ¯ ] (0 1 0). β-Ga 2 O 3 ( 1 ¯ 0 2 )||MgO(1 1 0) and β-Ga 2 O 3 [0 1 0] ⊥ MgO [0 0 1] for β-Ga 2 O 3 formed on (1 1 0) MgO. The β-Ga 2 O 3 formed on (1 1 1) MgO at 800 °C exhibited a threefold structure. The β-Ga 2 O 3 formed on (1 1 0) MgO had a twofold structure but different by 90° from the result reported previously. [ABSTRACT FROM AUTHOR]

A novel sintered tantalum carbide coating (SinTaC) prepared via a wet ceramic process is proposed as an approach to reducing the production cost and improving the crystal quality of bulk-grown crystals and epitaxially grown films of wide-bandgap semiconductors. Here, we verify the applicability of the SinTaC components as susceptors for chemical vapor deposition (CVD)-SiC and metal-organic chemical vapor deposition (MOCVD)-GaN epitaxial growth in terms of impurity incorporation from the SinTaC layers and also clarify the surface-roughness controllability of SinTaC layers and its advantage in CVD applications. The residual impurity elements in the SinTaC layers were confirmed to not severely incorporate into the CVD-SiC and MOCVD-GaN epilayers grown using the SinTaC susceptors. The quality of the epilayers was also confirmed to be equivalent to that of epilayers grown using conventional susceptors. Furthermore, the surface roughness of the SinTaC components was controllable over a wide range of average roughness (0.4 ≤ Ra ≤ 5 μm) and maximum height roughness (3 ≤ Rz ≤ 36 μm) through simple additional surface treatment procedures, and the surface-roughened SinTaC susceptor fabricated using these procedures was predicted to effectively reduce thermal stress on epi-wafers. These results confirm that SinTaC susceptors are applicable to epitaxial growth processes and are advantageous over conventional susceptor materials for reducing the epi-cost and improving the quality of epi-wafers. [ABSTRACT FROM AUTHOR]

Considerable interest in highly mismatched semiconductor alloys as materials for device applications has recently been shown. However, the spinodal instability can be a serious obstacle to their use. Here, the spinodal decomposition regions of dilute nitride In x Ga 1-x Sb y As z N 1-y-z , In x Ga 1-x Sb y P z N 1-y-z and In x Ga 1-x As y P z N 1-y-z quinary alloys lattice matched to III-V compounds are studied from 0 °C to 1000 °C. The alloys contain six types of chemical bonds corresponding to the constituent compounds, and rearrangement of atoms changes the bonds between them. Therefore, a size and location of the spinodal decomposition regions depend on the enthalpies of constituent compounds, internal strain energy, coherency strain energy and entropy. Among the considered alloys, In x Ga 1-x Sb y As z N 1-y-z lattice matched to InAs, In x Ga 1-x Sb y P z N 1-y-z lattice matched to GaP and InP and In x Ga 1-x As y P z N 1-y-z lattice matched to GaAs and InP are most suitable for device applications. [ABSTRACT FROM AUTHOR]

Selective area growth of GaN (SAG-GaN) films grown on nonpolar m-plane bulk GaN substrates using trench patterns was performed by metalorganic vapor phase epitaxy. We investigated the transformation of SAG-GaN facet structures by changing growth temperature, ambient, and miscut angle of substrates. Substrates with trench patterns along a -axis formed (10-11), (10-10), and (000-1) facet structures after SAG-GaN growth for growth conditions of 800 °C in N 2 +NH 3 and 1000 °C in H 2 +NH 3 ambience. Those with trench pattern along 45° off from a -axis contained (11-22), (10-10), (0-110) facet structures in substrates with a miscut angle of 5° whereas SAG-GaN films completely coalesced and formed smooth (10-10) surface in substrates with a miscut angle of 1°. Undesirable grains were formed for 800 °C in N 2 +NH 3 ambience regardless of the miscut angle of substrates whereas theses grains were annihilated using 1000 °C in H 2 +NH 3 ambience due to the intensively hydrogen etching. [ABSTRACT FROM AUTHOR]

Hillocks on N-face GaN (000 1 ¯ ) films are effectively eliminated by group-III-source flow-rate modulation epitaxy (FME), wherein the flow-rate of group-III sources are sequentially modulated under a constant supply of NH 3 . A hillock-free smooth surface obtained by group-III-source FME is attributed to the enhancement of step-flow growth. We found that a hillock originates from a micropipe and grows by spiral growth around the micropipe. The spiral growth rate rapidly decreases with decreasing the degree of surface supersaturation σ , while the step-flow growth rate decreases linearly. For group-III-source FME, wherein σ is lower than conventional continuous growth, the spiral growth rate could be lower than the step-flow growth one so that the formation of hillocks is suppressed. [ABSTRACT FROM AUTHOR]

Severe melt-back etching has forced the epitaxy of GaN on Si to use an AlN buffer layer for growing high-quality two-dimensional layers, despite its high resistivity. Herein, we report a metal-based pre-orienting layer (POL) for growing GaN nanostructures (NSs) to replace the traditional AlN buffer layer. Two metals, titanium (Ti) and hafnium (Hf), were evaluated as POLs. We succeeded in fabricating arrays of GaN NSs with highly preferred orientation using selective-area growth. The crystallographic phase of the POLs critically affected the evolved orientation of the crystals. Photoluminescence measurements revealed that GaN NSs with Hf-based POLs were of reasonably high quality. We believe that this result will facilitate broader III-V semiconductor applications using alternative substrates moving beyond conventional Si-based optoelectronics. [ABSTRACT FROM AUTHOR]

GaSb thin films were grown on quartz substrate and Ge(100) 1°-off-axis substrate by RF magnetron sputtering at growth temperatures of 400, 500, and 600 °C. The crystalline quality of GaSb/quartz improved with increasing growth temperature. The GaSb/Ge(100) grown at 500 °C exhibited good crystalline quality with comparatively high mobility (219 cm 2 /V s); however, the mobility degraded in GaSb/Ge(100) films grown at higher temperatures because of the increase in crystal defects induced by strain relaxation. Undoped GaSb has been previously reported to always exhibit p -type conductivity, irrespective of the growth method and growth conditions. However, we prepared an undoped GaSb thin film with n -type conductivity by using a Ge(100) 1°-off-axis substrate. This finding led to the conclusion that the use of an off-axis substrate affects the defect formation mechanism and enables the control of the conduction mechanism in undoped GaSb thin films. [ABSTRACT FROM AUTHOR]

The challenge to embed a single monolayer of phosphorus during epitaxial gallium arsenide (GaAs) growth triggers numerous questions regarding practical preparation, effective analysis, and fundamental consideration of the resulting interlayers. Beyond better understanding of III-V heterointerface formation processes, precise interlayer incorporation may enable enhanced interface design, effective diffusion barriers, and advanced band structure engineering. We employ metalorganic vapor phase epitaxy (MOVPE) in various growth modes (continuous, with interruptions, pulsed, surface exchange) targeting the most abrupt incorporation of thinnest GaP films in the GaAs(100) matrix. The intensities of higher order interference fringes in high resolution X-ray diffraction (HR-XRD) serve as a measure of the effective GaP x As 1−x film thickness and P concentration, which is compared to compositional analysis based on scanning transmission electron microscopy (STEM). In situ reflection anisotropy spectroscopy (RAS) provided us with insights to the GaAs(100) surface configurations relevant during the P interlayer preparation. [ABSTRACT FROM AUTHOR]

We report on the selective area vapor-liquid-solid (SA-VLS) growth of InP/GaP core shell nano-wires (NWs) by metal organic molecular beam epitaxy. Wurtzite crystal structure of the core InP was transferred to the GaP shell through layer by layer radial growth which eliminated bending of the NWs in random directions. Low growth temperature restricted surface segregation and kept the shell free from indium. Strain in the GaP shell was partially relaxed through formation of periodic misfit dislocations. From the periodicity of Moiré fringes and splitting of the fast-Fourier-transform of the transmission electron micrographs, the radial and axial strain were determined as 4.5% and 6.2%, respectively. [ABSTRACT FROM AUTHOR]

Our group works on improving the conversion efficiencies of terahertz (THz) wave generation using GaSe crystals. The operating principle is based on difference frequency generation (DFG) which has the advantages such as high output power, a single tunable frequency, and room temperature operation. In this study, GaSe crystals were grown by the temperature difference method under controlled vapor pressure (TDM-CVP). It is a liquid phase growth method with temperature 300 °C lower than that of the Bridgman method. Using this method, the point defects concentration is decreased and the polytype can be controlled. The transition metal Ti was used to dope the GaSe in order to suppress free carrier absorption in the low frequency THz region. As a result, a deep acceptor level of 38 meV was confirmed as being formed in GaSe with 1.4 at% Ti doping. Compared with undoped GaSe, a decrease in carrier concentration (~10 14 cm −3 ) at room temperature was also confirmed. THz wave transmittance measurements reveal the tendency for the absorption coefficient to increase as the amount of dopant is increased. It is expected that there is an optimum amount of dopant. [ABSTRACT FROM AUTHOR]

In recent years, a large interest has been reported on low-dimensional β-Ga 2 O 3 structures, like nanowires, nanobelts, nanorods or nanosheets, because of their peculiar and sometimes superior properties. These properties, however, can be strongly affected by the growth procedure, especially if metal growth catalysts are used. In this work we report the successful synthesis of β-Ga 2 O 3 nanowires/nanobelts using a simple combination of thermal evaporation of a metallic Ga source and controlled oxidation. The same growth procedure has been used to grow nanostructures on different kind of substrates (silicon and alumina), without catalyst as well as with Au or Pt deposited on the substrates, in order to promote the nucleation of nanowires. The morphological, structural and optical properties of the obtained nanostructures have been characterized and compared. Different growth distributions on the substrates and possible growth mechanisms have been highlighted, while a strong increase in luminescence intensity has been observed on samples grown with Au and Pt catalysts. [ABSTRACT FROM AUTHOR]

Here we report on the growth and characterization of β-Ga 2 O 3 bulk crystals and polycrystalline layer on different substrates. Bulk β-Ga 2 O 3 crystals were produced by free crystallisation of gallium oxide melt in sapphire crucible. Transparent single crystals measuring up to 8 mm across were obtained. Good structural quality was confirmed by x-ray diffraction rocking curve FWHM values of ~46″. Young’s modulus, shear modulus and hardness of the β-Ga 2 O 3 crystals were measured by nanoindentation and Vickers microindentation techniques. Polycrystalline β-Ga 2 O 3 films were deposited on silicon and sapphire substrates by sublimation method. It was found that structure and morphology of the films were greatly influenced by the material and orientation of the substrates. The best results were achieved on a -plane sapphire substrates where predominantly (111) oriented films were obtained. [ABSTRACT FROM AUTHOR]

Fe-doping of GaN layers of 3 in. in diameter and a thickness of 1 mm in a vertical AIX-HVPE reactor is studied. Ferrocen was used as Fe source. It is shown that a sufficient uniformity of growth conditions, a high purity of undoped GaN layers, and a moderate Fe incorporation of 2×10 18 cm −3 allow for growth of semi-insulating GaN layers with a sufficiently high specific resistivity even at elevated temperature. This makes the material suitable as substrate for electronic power devices at high power or in harsh ambient. [ABSTRACT FROM AUTHOR]

High crystallinity thick films with low free carrier concentration (≤1×10 15 /cm 3 ) and low compensation are required for many GaN-based electronic device applications. It has been demonstrated that low pressure chemical vapor and molecular beam epitaxy techniques can reproducibility deposit homoepitaxial films with low residual impurity concentrations. However, their typical slow growth rates prevent their utilization for thick film growth. Presently, hydride vapor phase epitaxy is the sole method that can deposit films with residual impurity concentrations ≤5×10 16 /cm 3 at hundreds of microns per hour growth rate. It is crucial to verify if this method can reproducibly deliver thick free-standing GaN films of high crystalline quality with exceptionally low and uniform free carrier concentration. X-ray diffraction, Raman scattering, and low temperature photoluminescence experiments were carried out on a number of samples prepared by dicing a free-standing wafer into several pieces perpendicular and parallel to the major growth directions; namely, c -plane {0001}, a -plane {11−20}, and m -plane {1−100}. SIMS depth profiles were employed to identify and quantify the concentration of the pervasive impurities. Spatial maps of a Raman line sensitive to free-carrier concentration were measured to determine the spatial distribution of the net impurity concentration. The reduced concentration of un-compensated shallow donors was also verified by low temperature electron paramagnetic resonance. [ABSTRACT FROM AUTHOR]

High-resistance GaN with low dislocation density adopting growth mode modification has been investigated by metalorganic chemical vapor deposition. The sheet resistance of the order of 10 16 Ω/sq has been achieved at room temperature by diminishing the oxygen impurity level close to the substrate with an AlN blocking layer. Attributed to this method which offers more freedom to tailor the growth mode, a three-dimensional (3D) growth process is introduced by adjusting the growth pressure and temperature at the initial stage of the GaN epitaxy to improve the crystalline quality. The large 3D GaN grains formed during this period roughen the surface, and the following coalescence of the GaN grains causes threading dislocations bending, which finally remarkably reduces the dislocation density. [ABSTRACT FROM AUTHOR]

Complex studies of intentional GaN carbon doping from propane during MOVPE were performed in a wide range of growth conditions. A strong dependence of carbon doping efficiency on growth rate and ammonia flow is revealed, while dependence of carbon doping efficiency on reactor pressure is small. Atomic force microscopy confirms the good quality of the GaN:C layers for doping levels as high as 2*10 19 cm −3 grown with growth rate up to 45 μm/h. The dependence of carbon incorporation into GaN is proportional to the propane concentration to the power 3/2 in most growth regimes, but for very high growth rate a linear or sub-linear component of the dependence becomes prominent. [ABSTRACT FROM AUTHOR]

A new approach to β-Ga 2 O 3 single crystal growth was studied, using the vertical Bridgman (VB) method in ambient air, while measuring the β-Ga 2 O 3 melting temperature and investigating the effects of crucible composition and shape. β-Ga 2 O 3 single crystals 25 mm in diameter were grown in platinum–rhodium alloy crucibles in ambient air, with no adhesion of the crystals to the crucible wall. Single crystal growth without a crystal seed was realized by (100) faceted growth with a growth direction perpendicular to the (100) faceted plane. [ABSTRACT FROM AUTHOR]

The selective area growth (SAG) of GaN was implemented on patterned GaN/sapphire templates by hydride vapor phase epitaxy (HVPE) to fabricate regular arrays of Ga-polar GaN microrods. The control of growth parameters such as H 2 /N 2 carrier gas ratio, growth temperature, and absolute NH 3 /HCl gas flow resulted in changes in the growth morphology. In particular, for an optimized mixed-carrier gas ratio of H 2 to N 2 , we achieved vertically well-aligned microrods. The topmost regions of the GaN microrods were terminated with pyramidal facets, indicating typical Ga polarity. The optical properties of the grown microrods were characterized by cathodoluminescence (CL) at a low temperature. This revealed that the GaN microrods had high crystal quality since they exhibited suppressed yellow luminescence as well as strong band edge emission. [ABSTRACT FROM AUTHOR]

The orientational relationship between β-Ga 2 O 3 and NiO was studied by X-ray diffraction measurements and cross-sectional high resolution transmission electron microscopy. A β-Ga 2 O 3 thin film was formed on a (100) NiO layer on a (100) MgO substrate by gallium evaporation in an oxygen plasma. It was found that the resulting β-Ga 2 O 3 had a four-fold domain structure satisfying both (100) β-Ga 2 O 3 ‖ (100) NiO and (010) β-Ga 2 O 3 ‖ {011} NiO. A γ-Ga 2 O 3 layer was observed at the interface between the β-Ga 2 O 3 and the NiO. An NiO film was also formed on a (100) β-Ga 2 O 3 single-crystal substrate by the sol–gel method. An epitaxial (100) NiO film was formed on a (100) β-Ga 2 O 3 substrate, and satisfied (011) NiO ‖ (010) β-Ga 2 O 3 . The crystal orientations of β-Ga 2 O 3 on (100) NiO and NiO on (100) β-Ga 2 O 3 can be explained using atomic arrangement models of the (100) plane of NiO and the (100) plane of β-Ga 2 O 3 . [ABSTRACT FROM AUTHOR]

Growth of gallium oxide thin films was carried out by Metalorganic Chemical Vapor Deposition (MOCVD) at different temperatures. Pure ε-phase epilayers of Ga 2 O 3 , with good morphology and structural properties, were obtained, for the first time with this technique, on sapphire at the temperature of 650 °C. XRD analysis performed by high-resolution diffractometry confirmed the good crystallographic quality of the grown layers. At temperatures higher than 700 °C the usual stable β-Ga 2 O 3 phase was obtained. The ε-films were successfully deposited also on (0001)-oriented GaN and (111)- and (001)-oriented 3C–SiC templates, provided that the appropriate temperature was chosen. This indicates that the temperature, rather than substrate structure, is the growth parameter which decides what phase actually forms. The growth proceeds via coalescence of hexagonal islands and is favored when a substrate with an in-plane hexagonal arrangement of the atoms is employed. By applying Atomic Layer Deposition (ALD), epitaxial growth of the ε-phase was achieved at lower temperature, while the overall uniformity resulted improved, even on large sapphire substrates. [ABSTRACT FROM AUTHOR]

The effects of an amorphous interfacial silicon nitride (Si X N Y ) layer on the morphology, structure and optoelectronic properties of GaN nanowires (NWs), grown on Si (111) substrates by plasma assisted molecular beam epitaxy, have been investigated. The unintentional Si nitridation, during the first stages of direct GaN NW growth on the bare Si surface, has been compared to intentional Si nitridation prior to GaN growth. The intentional nitridation resulted in a uniform ~1.5 nm amorphous Si X N Y interlayer at the GaN/Si interface, while an irregular and non-uninform interface, with partial presence of amorphous Si X N Y, appeared for direct GaN on Si growth. The homogeneity of the interfacial structure enhanced the degree of crystallographic alignment of the GaN NWs, concerning both tilt and twist. It also decreased the dispersion of NW heights that is otherwise triggered by different nucleation times on structurally different sites of the substrate. The average height of the NWs was similar for both cases but their average diameter was increased from 25 nm to 40 nm on the uniform amorphous Si X N Y interlayer, possibly an effect of weak epitaxial constraints. Reduced overall intensity and increased defect-related emission at 3.417 eV characterized the 20 K photoluminescence spectra for direct GaN growth on Si. The results contribute to a better understanding of how the GaN/Si interfacial structure affects the GaN NW growth and properties. [ABSTRACT FROM AUTHOR]

The initially dry-etched GaN layer with trapezoidal cross-section was laterally etched along the 〈11 2 ¯ 0〉 direction in the tetramethyl ammonium hydroxide (TMAH) solution to form a sidewall normal to the direction, which is corresponding to the (11 2 ¯ 0) plane. On the other hand, the etched sidewall still maintains the trapezoidal shape with angle of 58.4° when etched along the 〈1 1 ¯ 00〉 direction, which is corresponding to the (1 1 ¯ 01) plane. The GaN lateral nanowires with two different types of cross-sections, Ω-shape which is connected to underlying thick buffer layer through very narrow neck region and rectangle shape which is completely separated from underlying buffer layer, were realized with second lateral TMAH wet etching along the 〈11 2 ¯ 0〉 direction and by using the atomic layer deposited (ALD) HfO 2 layer as a sidewall spacer. The shape is dependent on both the height of the second dry-etched GaN sidewall below the HfO 2 spacer and the second wet etching time in TMAH solution. It was found that the dangling bond density at the surface of the crystal plane is responsible for the strong lateral anisotropic etching property of the GaN layer in TMAH solution. [ABSTRACT FROM AUTHOR]

GaAsP has important applications for solar cells and light-emitting diodes on silicon substrates. Here we demonstrate that GaAsP can be directly grown by metal-organic chemical vapor deposition on previously-prepared lattice-matched SiGe virtual substrates, without prior in-situ growth of SiGe. By optimizing the growth pressure and AsH 3 pre-exposure time, the surface morphology of GaAsP is improved and the pinhole densities are reduced by two orders of magnitude from 2.4×10 7 /cm 2 to 1.2×10 5 /cm 2 . The physics is suggested to be an optimization between complete As-termination and AsH 3 etching effect of SiGe surface. [ABSTRACT FROM AUTHOR]

GaN thin films were grown on Al 2 O 3 (0001) by MBE using NH 3 -clusters either ionized with the energy of 4–7 eV/molecule (ionized Cluster Beam, i-CB) or un-ionized with the energy of about 0.1 eV/molecule (neutral Cluster Beam, n-CB) at growth temperatures ranging from 390 to 960 °C. The c-axis is extremely elongated but the a -axis is shrunken at the initial growth stage (up to the film thickness of about 10 nm) in GaN grown by the mixture of n- and i-CB under N-rich condition. The films thicker than 30 nm have the relaxed a - and c -axis lengths close to the unstrained values and obey the Poisson relation. GaN grown by i-CB under Ga-rich condition have the relaxed lattice constants obeying the Poisson relation for the film as thin as 6 nm. In GaN grown by the cluster beam (CB) which is not ionized intentionally, both a- and c-axis lengths are almost independent of the film thickness, having nearly the same values as those of the unstrained samples. These characteristics can be ascribed to the nature of interface between the nitrided Al 2 O 3 substrate and epilayer. It is concluded that the films grown by i-CB bond firmly to underlay AlN than the films by n-CB and CB. [ABSTRACT FROM AUTHOR]

The effects of doping with silicon (Si) AlGaAs layers grown by molecular beam epitaxy on GaAs (6 3 1)-oriented substrates as a function of the arsenic pressure ( P As ) is presented and compared with layers grown on (1 0 0) oriented substrates. The surface texture of the AlGaAs (6 3 1) films is composed by nanogrooves, whose dimensions depend on P As. On the contrary, the MBE growth on the (1 0 0) plane resulted on rough surfaces, without evidence of formation of terraces. Mobility and carrier density of AlGaAs:Si layers grown on substrates (6 3 1) were studied as a function of P As . The doping type conversion from p-type to n-type as a function of the As pressure is corroborated for high index samples. All the films grown on (1 0 0) exhibited silicon n-type doping. These observations were related with the amphotericity of Si, where it acts as a donor impurity occupying Al or Ga-sites or as an acceptor when it takes an As-site, depending on the competition that the Si atoms encounters with As for any of these sites. The acceptor and donor lines close to the AlGaAs transition observed by photoluminescence spectroscopy (PL) were affected by the incorporation of Si. When increasing P As the energy of the main PL peak is redshifted for n-type AlGaAs layers, but it is shifted back towards high energy once the conduction type conversion takes place. X-ray diffraction patterns revealed high crystalline quality for samples grown at the highest P As . [ABSTRACT FROM AUTHOR]

We report structural, electrical, and optical properties of Si-doped γ-Ga 2 O 3 films epitaxially grown on (100) MgAl 2 O 4 substrate by pulsed-laser deposition. The γ-Ga 2 O 3 :Si films of a metastable spinel phase had neither secondary phase nor rotation domain. A highly doped film exhibited n-type conductivity with a carrier concentration of 1.8×10 19 cm −3 and a Hall mobility of 1.6 cm 2 V −1 s −1 at 300 K. Donor activation energy was estimated to be less than 7 meV from nearly temperature-independent transport properties down to 77 K. The successful impurity doping indicates that γ-Ga 2 O 3 can be used as an n-type wide-band-gap semiconductor. [ABSTRACT FROM AUTHOR]

One-temperature and two-temperature synthesis methods for GaSe, a nonlinear optical compound, were developed. X-ray diffraction showed that pure α-GaSe was synthesized. By Vertical Bridgman method using spontaneous nucleation the GaSe single crystals were grown with diameter 20–25 mm and length 40–45 mm and yield ~60%. The rocking curve for the studied GaSe sample was symmetric and its FWHM did not exceed 3′, which corresponds to the dislocation density at the level of 10 12 –10 13 cm −2 . SEM showed imperfections of surface of non-etched cleaved GaSe. According the obtained data the absorption coefficient at 1.06 μm and 2 μm is ~0.1 cm −1 . At 9.3–10.9 μm for nonpolarized light the calculations give absorption coefficient ~0.1–0.12 cm −1 . [ABSTRACT FROM AUTHOR]

• β-(Sc x Ga 1- x) 2 O 3 (x = 0.062, 0.082) was grown via Czochralski and vertical gradient freeze methods. • Nuclear magnetic resonance shows octahedral site preference. • Crystals demonstrated increased bandgap, although lower efficiency than alumina alloying. • Stark manifold luminescence present from rare earth element impurities. β-Ga 2 O 3 is an emergent ultrawide bandgap material, which has been recently studied with respect to alumina alloying in order to tailor the bandgap for thin film or bulk applications. In this work, bulk Czochralski and vertical gradient freeze crystals of 6 – 8 mol.% Sc 2 O 3 alloyed β-Ga 2 O 3 (SGO) – β-(Sc 0.06 Ga 0.94) 2 O 3 to β-(Sc 0.08 Ga 0.92) 2 O 3 – were obtained, which showed a nominal + 0.07 eV increase in the optical bandgap compared to unintentionally doped (UID) β-Ga 2 O 3. SGO was characterized for structure (X-ray diffraction, rocking curve, nuclear magnetic resonance, Raman microscopy), purity (glow discharge mass spectrometry, X-ray fluorescence), optical transmission (200 nm – 25,000 nm), resistivity, and luminescence (laser induced luminescence microscopy, photoluminescence). Structural measurements indicate successful incorporation of Sc, although overall lower quality than UID and β-(Al 0.1 Ga 0.9) 2 O 3 (AGO) material. Purity and optical measurements demonstrated few acceptor impurities and a widened band gap, although not wide enough for some donors to become deep enough to promote insulating behavior. Bulk SGO crystals demonstrated intense Stark luminescence transitions characteristic of Nd3+, presumably an impurity in the Sc 2 O 3 powder, with some areas of the crystal showing highly concentrated Nd3+. Despite demonstrating an enlarged bandgap, scandia alloyed β-Ga 2 O 3 retained electrical conduction similar to UID β-Ga 2 O 3 , unlike alumina alloyed β-Ga 2 O 3 which was electrically insulating. [ABSTRACT FROM AUTHOR]

In this study, wurtzite gallium nitride (GaN) thin film was directly grown on hexagonal silicon carbide (6H–SiC) substrate without buffer layer using sol–gel spin coating method followed by annealing and nitridation process. The entire growth process was investigated in-depth. The results revealed that the conversion of GaN thin film proceeds through an intermediate of amorphous gallium(I) sub-oxide (Ga 2 O). In this case, the amorphous Ga 2 O was converted into GaN thin film after being nitridated at 950 °C under ammonia ambient. The intermediate of amorphous Ga 2 O can only be identified through infrared reflectance measurements. [ABSTRACT FROM AUTHOR]

We demonstrate the high-speed growth of β-Ga 2 O 3 quasi-heteroepilayers on off-angled sapphire (0 0 0 1) substrates by halide vapor phase epitaxy (HVPE). ( 2 ¯ 0 1 ) oriented β-Ga 2 O 3 layers were successfully grown using GaCl and O 2 as source gases. The growth rate monotonically increased with increasing the partial pressures of the source gases, reaching over 250 μm/h. This rate is over two orders of magnitude larger than those of conventional vapor phase epitaxial growth techniques such as molecular beam epitaxy or metalorganic vapor phase epitaxy. X-ray pole figure measurements indicated the presence of six in-plane rotational domains, in accordance with the substrate symmetry, plus some minor (3 1 0) domains. By the use of off-angled substrates and thick layer overgrowth, one of the in-plane orientations was strongly favored and the (3 1 0) residuals effectively suppressed, so that quasi-heteroepitaxial growth was achieved. Therefore, these results indicate the high-potential of the HVPE technique for the growth of thick and thin β-Ga 2 O 3 layers for the cost-effective production of β-Ga 2 O 3 based devices. [ABSTRACT FROM AUTHOR]

This paper presents the results of pulsed-GaCl flow modulation epitaxy (FME) on hydride vapor phase epitaxy (HVPE) at various interval times, supply times, and V/III ratios under a constant NH 3 flow. The best performance was observed at an interval time of 30 s, GaCl gas supply time of 10 s in one cycle and V/III ratio of 10. As compared to the conventional HVPE growth, the utilization efficiency of the GaCl gas improved by 2.5 times in the present method and the root-mean-square (RMS) values reduced to one-fifth of the original, without degradation of crystalline quality. We concluded that the dynamic change in the V/III ratio in one cycle of an FME sequence contributed to a change in the growth mode, resulting in an improved utilization efficiency of the GaCl gas. [ABSTRACT FROM AUTHOR]

Single crystals of lithium tetra-amidogallate, Li[Ga(NH 2 ) 4 ], were obtained from the reaction of Ga metal and LiNH 2 in supercritical ammonia at a pressure of 250 MPa and temperature of 400 °C. Two structural modifications were characterized by single crystal X-ray diffraction: a =5.849(1) Å, b =12.640(3) Å, c =6.858(1) Å, β =92.56(3)°, Z =4, space group P 2 1 / n ; a =6.005(1) Å, b =7.394(2) Å, c =6.005(1) Å, β =103.51(3)°, Z =2, space group P 2 1 . Disodium tetra-amidogallate amide, Na 2 [Ga(NH 2 ) 4 ]NH 2 ( a =11.748(2) Å, b =6.681(1) Å, c =9.665(2) Å, Z =4, space group Pnma ) , was grown ammonothermally ( p =130 MPa, T =580 °C) as single crystals in the course of synthesizing wurzite GaN employing NaNH 2 as an ammono-basic mineralizer. Like known Na[Ga(NH 2 ) 4 ], all three novel compounds contain isolated tetra-amidogallate ions [Ga(NH 2 ) 4 ] − as constituents and likely candidates for dominant dissolved gallium-containing species in ammonothermal GaN synthesis and crystal growth under ammono-basic conditions, accomplishing the material transport. Raman spectroscopy data for Li[Ga(NH 2 ) 4 ] in both modifications as well as Na 2 [Ga(NH 2 ) 4 ]NH 2 are provided and discussed. [ABSTRACT FROM AUTHOR]

Polarized Raman spectra were measured from (010) Mg-doped, (100) Si-doped, and (001) unintentionally-doped β-Ga2O3 substrates prepared by either the floating zone growth or edge-defined film-fed growth methods. The Ag and Bg Raman active modes were perfectly separated in the spectra according to the polarization selection rules. To the best of our knowledge, this is the first experimental observation of a complete set of polarized Raman spectra of β-Ga2O3. The results are ensured by the high uniformity of crystalline orientation and surface flatness of the present substrates. [ABSTRACT FROM AUTHOR]

Abstract: Gallium oxide nanostructures with high aspect ratio and variable faceting were synthesized by the chemical vapor deposition method via vapor–solid growth mechanism. Systematic investigation of the growth conditions revealed that these nanowires can be produced under the conditions of high temperature and low precursor flow. The nanowires crystalize as the β-phase Ga2O3, which has the monoclinic crystal structure. Preferred growth was along the [010] direction, as corroborated with lattice-resolved imaging and crystal plane models. The high degree of faceting is discussed in terms of the evolution of the nanowire cross section morphology, based on the growth rate of the facet boundaries relative to the nanowire surface planes. The obtained nanowires show intense blue emission, characterized by a broad-band photoluminescence spectrum with a maximum at 430nm and long decay time. This emission arises from the defect-related donor-acceptor pair recombination mechanism, and depends on the nanostructure dimensionality and morphology. The possible influence of controlled nanowire faceting on the observed optical properties is also discussed. Owing to their morphology-dependent optical properties, these nanowires are promising building blocks for electronic and optoelectronic structures and devices. [Copyright &y& Elsevier]

Abstract: We developed high-temperature autoclaves which are capable of growing GaN crystals at temperature <850°C and pressure <150MPa. A high-temperature acidic ammonothermal method with acidic mineralizer revealed retrograde solubility of GaN, and yielded GaN crystals with XRC-FWHM values of around 30″. [Copyright &y& Elsevier]

Previously, we succeeded in growing flat semipolar {11−22} GaN layers on an r-plane patterned sapphire substrate (r-PSS). However, the GaN layers still contain a dislocation density of over 3×108/cm2 and stacking faults (SFs). To reduce such defects, we employed shallowly etched r-PSSs. The etching depths of the shallowly etched r-PSSs were from 100 to 500nm, whereas that of a conventional r-PSS was 1μm. As a result, we found that the threading dislocation density (TDD) decreases as the etching depth decreases. The TDD of the {11−22} GaN layer on r-PSS etched to a depth of 100nm was 1.3×108/cm2. Moreover, the reduction of the SFs was observed by photoluminescence at cryogenic temperature. The reduction of the defects revealed the growth mechanism; the crystalline quality of {11−22} GaN on an r-PSS depends on the selective growth area of the sapphire sidewall. [ABSTRACT FROM AUTHOR]

Abstract: 100nm thick GaAsBi layers were grown at a range of temperatures using both As2 and As4. Measurements of Bi incorporation based on room temperature photoluminescence spectra indicate that the growth temperature dependence of Bi incorporation is the same for both As species and is invariant with respect to Bi flux; however, Bi incorporation saturates when the growth temperature is low enough for the Bi incorporation coefficient to reach unity. The As:Ga atomic flux ratios allowing significant Bi incorporation are coincident for both As species upon accounting for desorption of 50% of the incident As4 atoms during GaAs growth. The Bi reconstruction lifetime at 415°C was measured under overpressures of both As species and under vacuum. The lifetime is significantly longer than the monolayer growth time used in this work; however, results do show that As2 is more aggressive at displacing Bi from a static surface than As4. The photoluminescence intensities of the samples grown in this work vary with Bi incorporation in accordance with current literature and appear to be independent of As species. [Copyright &y& Elsevier]

Abstract: AgGa1−x In x Se2 (x=0.5) polycrystalline material was successfully synthesised from high purity elements by the melt and temperature oscillation method. Large size and crack-free AgGa0.5In0.5Se2 single crystals were grown using a double wall quartz ampoule with accelerated crucible rotation technique (ACRT) by modified vertical Bridgman method. The unit cell parameters were confirmed by single crystal X-ray diffraction analysis. The composition of AgGa0.5In0.5Se2 was measured using energy dispersive spectrometry (EDS). The insignificant change in atomic percentages of Ag, Ga, In and Se along the ingot further reveals that the composition throughout its length is fairly homogeneous. The transmittance spectra of AgGa0.5In0.5Se2 single crystal was achieved in the NIR region and high transmittance of the crystals in the mid-IR region was revealed. The absorption edge of the material is near 881nm and the optical band gap energy is 1.4eV. Thermal property of AgGa0.5In0.5Se2 has been studied using Differential scanning calorimetry (DSC) technique and it confirms that the increase in Indium content reduces the super-cooling temperature. Electrical property is measured using Hall Effect measurements and it confirms the n-type semiconducting nature. [Copyright &y& Elsevier]

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]