Tri-halide Vapor Phase Epitaxy Research Articles

Investigation of high speed β-Ga2O3 growth by solid-source trihalide vapor phase epitaxy

Trihalide vapor phase epitaxy (THVPE) is a new type of halide vapor phase epitaxy (HVPE) that uses GaCl3 as a group III source, enabling Ga2O3 growth without particle generation, although the growth rate is low. In this study, β-Ga2O3 is grown by THVPE using solid GaCl3 as a group III precursor. The growth rate increases linearly with increasing partial pressure of the precursor. The dependence of the growth rate on the VI/III ratio is revealed on sapphire substrates, with the growth rate reaching a maximum at a VI/III ratio of 95. We have also obtained a growth rate of 32.2 μm h−1 on β-Ga2O3 (001) substrates with no particle generation, crystal quality equivalent to that of the substrate, and high purity equivalent to that of HVPE.

The Introduction of Intermediate Layers for InGaN Growth on ScAlMgO4 through Trihalide Vapor‐Phase Epitaxy

Herein, the effect of intermediate layers for high‐speed InGaN growth using trihalide vapor‐phase epitaxy (THVPE) on ScAlMgO4 (SAM) is investigated. The coverage and thickness of the intermediate layer have a significant impact on both composition and crystalline quality. Herein, InGaN is successfully fabricated with 17% of indium on SAM in a lattice‐matched state employing THVPE, showing the X‐ray rocking curve full width at half maximum values less than 1000 arcsec, in a two‐step growth. THVPE is used to indicate the possibility of fabricating high‐quality InGaN quasi‐substrate with high indium composition.

Suppression of cluster formation in GaN growth by tri-halide vapor phase epitaxy with external GaCl3 gas supply system

One critical issue hindering high-quality, high-speed growth of GaN is cluster formation in the gas phase. We investigated cluster formation in tri-halide vapor phase epitaxial growth of GaN. The growth system is equipped with an external GaCl3 gas supply system. We observed cluster formation under certain growth conditions experimentally. A simulation was also carried out to reveal the critical conditions for cluster formation. We propose that increasing the gas temperature is an effective way to suppress cluster formation, and thus achieve a higher growth rate with a flat surface morphology.

Growth of lattice-relaxed InGaN thick films on patterned sapphire substrates by tri-halide vapor phase epitaxy

Lattice-relaxed thick InGaN films could be obtained using patterned sapphire substrates (PSSs) by tri-halide vapor phase epitaxy. Furthermore, by inserting the GaN intermediate layer between the InGaN epilayer and the PSS, the crystalline quality of the InGaN epilayer was drastically improved. According to the X-ray diffraction ω-rocking curve measurements, the full width at half maximum of the InGaN epilayer was 850 arcsec around the symmetrical reflection and 967 arcsec around the skew-symmetrical reflection. It was also found that the thickness of the GaN intermediate layer influences the crystalline quality of the InGaN epilayer. As the thickness of the GaN intermediate layer increases, the crystalline quality of the GaN intermediate layer gets higher, resulting in the crystalline quality of the InGaN epilayer was improved.

Homo- and hetero-epitaxial growth of β-gallium oxide via GaCl3-O2-N2 system

β-gallium oxide (Ga2O3) was grown by tri-halide vapor phase epitaxy (THVPE) using gaseous GaCl3 and O2 as precursors. The growth rate linearly increased with increasing ratios of input partial pressure of O2 against GaCl3, and further, it was found the β-Ga2O3 growth by THVPE successfully suppressed the gas phase reaction and decreased Ga2O3 particles observed in halide vapor phase epitaxy (HVPE) by changing the ratio of the supply partial pressure of the second chlorine against that of the first during the GaCl3 generation. An epilayer with high crystalline quality and high purity equivalent to that grown via HVPE was obtained by newly developed THVPE without any particle formation.

Facet stability of GaN during tri-halide vapor phase epitaxy: anab initio-based approach

Anab initio-based approach is used to study the facet stability of GaN during THVPE. The surface phase diagrams as functions of temperature and pressure are determined. Wulff construction is used to predict the crystal shape.

Growth of Highly Crystalline GaN at High Growth Rate by Trihalide Vapor‐Phase Epitaxy

Free‐standing gallium nitride (GaN) wafers are being increasingly used for high‐power and high‐frequency electronic devices. However, these have to be produced at low costs while maintaining high quality. With the aim of reducing the cost of manufacturing GaN substrates, trihalide vapor‐phase epitaxy (THVPE) is investigated to explore the effect of growth temperatures up to 1400 °C. High growth rate and high crystal quality are achieved simultaneously using THVPE. High‐quality GaN crystals are obtained at the growth rate of more than 300 μm h−1. Crystal characteristics are confirmed via the full width at half maximum (FWHM) of the (002) plane, obtained by the X‐ray two‐crystal (XRC) method. Dark spot density (DSD) measured via cathode luminescence decreases to the level of seed substrate at growth temperatures above 1300 °C. The yellow emission band is not visible in the photoluminescence spectra of the 2 in.‐diameter sample, which is consistent with very small concentrations of carbon impurities in the crystal. In addition to the attainment of high‐purity materials, parasitic polycrystal growth around the wafer and the reactor wall is eliminated, which can improve the productivity of the THVPE, due to very little down time of the reactor.

Growth of GaN on a three-dimensional SCAATTM bulk seed by tri-halide vapor phase epitaxy using GaCl3

GaN with a film thickness of 200–600 μm was grown on the as-grown three-dimensional supercritical acidic ammonia technology (SCAATTM) bulk seed that comprised only semipolar planes at a temperature as high as 1390 °C by tri-halide vapor phase epitaxy; further, the GaN film was also characterized. The FWHM value of the X-ray rocking curves was ∼40″, which was almost similar to the value of the used seed. The curvature radii were as large as 40–64 m. Further, the carrier concentrations were observed to be as small as 5.1 × 1017–9.1 × 1017 cm−3. However, the basal plane stacking fault densities were observed to be 3.4 × 101–5.4 × 101 cm−1 and were observed to increase during the growth process because of the as-grown SCAATTM seed surface condition.

GaN epitaxial growth on 4 degree off-axis Si- and C-face 4H-SiC without buffer layers by tri-halide vapor-phase epitaxy with high-speed wafer rotation

The results of GaN epitaxial crystal growth on 4° off-axis Si- and C-face 4H-SiC without buffer layers by tri-halide vapor-phase epitaxy (THVPE) with high-speed wafer rotation and the properties of the obtained material are briefly described in this paper. GaN epitaxial layers were grown on 4° off-axis 4H-SiC(0001)Si and 4H-SiC(000-1)C substrates. The obtained material’s properties were studied by Nomarski optical microscopy, scanning electron microscopy, photoluminescence, surface two-photon excitation microscopy, X-ray diffraction and Raman spectroscopy. The structural and optical properties of the GaN epitaxial layer are presented and discussed. By adopting an external GaCl3 material supply system, high-speed rotation was applicable, and its effect was confirmed. The results show that when THVPE was used under growth pressure of 600 mbar at 900 °C–950 °C, the surface reaction rate was sufficiently high, and the GaN epitaxial layer was grown under conditions of controlled raw-material supply rates. High growth rates (40–50 μm h−1) and relatively low threading dislocations (∼7 × 107 cm−2) were achieved on 4° off 4H-SiC(000-1)C despite the large lattice mismatch (3.1%) between SiC and GaN and without any buffer layers by introducing step flow growth and growth on a high-quality 4H-SiC substrate. We found that epitaxial layers with a smooth surface morphology can be grown on 4H-SiC(000-1)C compared with growth on 4H-SiC(0001)Si.

Influence of intermediate layers on thick InGaN growth using tri-halide vapor phase epitaxy

A thick and fully relaxed In0.05Ga0.95N layer was epitaxially grown on a GaN substrate after growing partially relaxed intermediate InGaN layers using tri-halide vapor phase epitaxy. In order to control the relaxation ratio of intermediate InGaN layers, a double intermediate structure with different growth rates (low growth rate and high growth rate modes) was adopted. By changing the first intermediate InGaN layer thickness, the relaxation ratio could be varied in the ranges between 25% and 59%. According to X-ray diffraction reciprocal space mapping measurements, a fully relaxed In0.05Ga0.95N layer was successfully grown on a partially relaxed intermediate In0.10Ga0.90N layer with the relaxation ratio of 32%. Thus, a mirror-like, fully relaxed and thick In0.05Ga0.95N layer could be grown with lattice matched to the intermediate InGaN layers by controlling the relaxation ratio.

GaN growth via tri-halide vapor phase epitaxy using solid source of GaCl3: investigation of the growth dependence on NH3 and additional Cl2

Gallium nitride (GaN) growth via a tri-halide vapor phase epitaxy method using a solid source of GaCl3 and gaseous NH3 was investigated both on Ga-polar and N-polar GaN templates. The relationship between gallium precursor molecule and growth polarity was clarified; it was found that a small amount of GaCl3 could be reduced by H2 originating from the decomposition of NH3 to produce GaCl, and additional Cl2 could suppress the reduction process. Accordingly, GaCl3 was found to be a proper Ga precursor for N-polar GaN growth, whereas GaCl was the proper precursor for Ga-polar GaN growth. The state of the Ga precursor molecule could be predicted by thermodynamic analysis. Furthermore, the decomposition ratio of NH3 could be determined by a combination of the experimental results and the calculated value of the thermodynamic analysis.

Growth temperatures and the excess chlorine effect of N-Polar GaN growth via tri-halide vapor phase epitaxy

In this paper, we investigated the effects of the growth temperature and chlorine gas on the growth of thick GaN on an N-polar GaN substrate via tri-halide vapor phase epitaxy. The results revealed that free Cl2 is necessary for high-speed growth. When the growth temperature increases, the crystal quality improves, and a high growth rate and high crystalline quality can be simultaneously achieved.

Quasiequilibrium crystal shape and kinetic Wulff plot for GaN grown by trihalide vapor phase epitaxy using GaCl3

We demonstrated the selective‐area growth (SAG) of the nonpolar m‐plane and the polar −c‐plane substrates to determine the quasiequilibrium crystal shape (quasi‐ECS) by trihalide vapor phase epitaxy (THVPE). The results were compared with those by hydride vapor phase epitaxy (HVPE). The polar N‐face and the nonpolar m‐planes were consistently stable with the semipolar planes emerging only at high temperature for the quasi‐ECS grown by THVPE. The clear facets of the polar Ga‐face (0001) and Ga‐face sense semipolar planes such as did not appear. The kinetic Wulff plots for THVPE were constructed using the growth velocities for each emerging facet of the SAG.Bird's‐eye view SEM images of the selective‐area GaN crystals grown on the m‐plane and –c‐plane for THVPE.

Thick nonpolar m-plane and semipolar [formula omitted] GaN on an ammonothermal seed by tri-halide vapor-phase epitaxy using GaCl3

GaN layers of thickness 0.5–1.3mm were grown at 1280°C at a growth rate of 95–275µm/h by tri-halide vapor-phase epitaxy on nonpolar m-plane (101̅0) and semipolar (101̅1̅) ammonothermal GaN substrates. For nonpolar m-plane (101̅0) with a −5° off-angle, the full widths at half maximum (FWHMs) of X-ray rocking curves (XRCs) and the basal plane stacking fault (BSF) density increased from 50 to 178″ and from 4.8×101 to 1.0×103cm−1, respectively, upon increasing the growth rate from 115 to 245µm/h. On the other hand, the XRC-FWHM and the BSF density for semipolar (101̅1̅) grown at 275µm/h were as small as 28″ and 8.3×101cm−1, respectively.

Tri-halide vapor-phase epitaxy of GaN using GaCl3 on polar, semipolar, and nonpolar substrates

Homoepitaxial tri-halide vapor-phase epitaxy (THVPE) growth on polar, semipolar, and nonpolar bulk GaN substrates was demonstrated using GaCl3 as the precursor. The influence of the surface orientation of the substrate on GaN growth by THVPE was compared with that observed for GaN grown by hydride vapor-phase epitaxy. The dependence of the GaN growth on the surface orientation of the substrate was confirmed; GaN could be grown on , , , , and but not on , , , or . This behavior was explained to be due to the changes in adsorption energy, the magnitudes of which were estimated by theoretical calculations.

Tri-halide vapor phase epitaxy of thick GaN using gaseous GaCl3 precursor

Tri-halide vapor phase epitaxy (THVPE) of thick GaN using GaCl3 was investigated for fabricating low-cost, high-crystalline-quality GaN substrates instead of the conventional manufacturing method of GaCl-based hydride vapor phase epitaxy (HVPE). The growth rate and upper growth temperature limit of GaN using THVPE were found to be much higher than those obtained using conventional HVPE under the same growth conditions. Drastic reduction in the number of dark spots measured by cathodoluminescence at room temperature was observed for the high-temperature-grown GaN layer on the (000-1) GaN/sapphire template due to the enhancement of precursor migration on the growing surface. It was found that the incorporation of impurities such as O, C, and Cl can be reduced even on the N-polarity GaN by increasing the growth temperature. The possibility of enlargement of the crystal diameter by growing the N-polarity GaN layer using THVPE was also proposed.

Growth of thick and high crystalline quality InGaN layers on GaN (0001¯) substrate using tri-halide vapor phase epitaxy

The growth of thick InGaN layers on free-standing GaN (0001¯) substrates was studied using tri-halide vapor phase epitaxy. It was found that high-indium-content InGaN can be grown under higher InCl3 input partial pressure at higher growth temperature, which allows the fabrication of a high crystalline quality InGaN layer with a smooth surface morphology. Using the growth conditions of high InCl3 input partial pressure and high growth temperature, crack- and droplet-free InGaN layers with a thickness of over 10µm and with an indium fraction of 0.05 were successfully grown. Although the surface showed many hillocks, the number of hillocks was reduced upon growth of thicker InGaN layers. Photoluminescence measurements confirm that thick InGaN layers could be successfully grown without degradation of the crystalline quality.

Investigation of NH3 input partial pressure for N-polarity InGaN growth on GaN substrates by tri-halide vapor phase epitaxy

The influence of NH3 input partial pressure on N-polarity InGaN grown by tri-halide vapor phase epitaxy was investigated. It was found that surface morphology, solid composition and optical properties were affected by NH3 input partial pressure. As shown in thermodynamic analyses, the indium content increased due to an increase in the driving force for InN deposition caused by increased NH3 input partial pressure. In addition, the deep level emission around 2.1 eV in photoluminescence measurements drastically decreased at higher NH3 input partial pressures. Ab initio calculations and subsequent secondary ion mass spectrometry measurements suggested the reduction of metal-vacancies and/or carbon impurity incorporation in the InGaN layers.

Growth of thick InGaN layers by tri-halide vapor phase epitaxy

This is the first study to report InGaN growth by tri-halide vapor phase epitaxy (THVPE) using InCl3 and GaCl3 generated by the reactions between metal sources (i.e., metallic indium and gallium) and gaseous chlorine. The influence of the surface orientation of the initial substrate on InGaN-THVPE growth was investigated using freestanding (0001) and GaN substrates. Only a N-polar InGaN epitaxial layer was obtained by THVPE because of the instability of GaCl3 adsorption toward nitrogen atoms on the Ga-polar surface. In addition, we investigated the influence of the group-III input partial pressure on the growth rate and solid composition of InGaN layers grown on a GaN substrate. The growth rate increased linearly with group-III concentration, and a maximum growth rate of 15.6 µm/h was achieved at PIII = 2.0 × 10−3 atm.

Thermodynamics on tri-halide vapor-phase epitaxy of GaN and In xGa 1− xN using GaCl 3 and InCl 3

Thermodynamic analyses on tri-halide vapor-phase epitaxy (THVPE) of GaN and In x Ga 1− x N using GaCl 3 and InCl 3 are described. The partial pressures of gaseous species in equilibrium with GaN and In x Ga 1− x N and the driving force for the deposition are calculated for growth temperature and the hydrogen mole fraction in the carrier gas. It is shown that the deposition of GaN and In x Ga 1− x N is significantly influenced by the hydrogen mole fraction in the carrier gas. The vapor-solid distribution relationship of In x Ga 1− x N alloy deposition using GaCl 3 and InCl 3 is discussed in comparison with the experimental data reported in the literature. It is shown that the solid composition x in In x Ga 1− x N is thermodynamically controlled.