Growth of GaN on SiC/Si substrates using AlN buffer layer by hot-mesh CVD

GaN films were grown on SiC/Si (111) substrates by hot-mesh chemical vapor deposition (CVD) using ammonia (NH₃) and trimetylgallium (TMG) under low V/III source gas ratio (NH₃/TMG = 80). The SiC layer was grown by a carbonization process on the Si substrates using propane (C₃H₈). The AlN layer was deposited as a buffer layer using NH₃ and trimetylaluminum (TMA). GaN films were formed and grown by the reaction between NH_x radicals, generated on a tungsten hot mesh, and the TMG molecules. The GaN films with the AlN buffer layer showed better crystallinity and stronger near-band-edge emission compared to those without the AlN layer.     

Deposition of GaN films on (1 1 1) Si substrates by alternate supply of TMG and NH3

GaN films were grown on (1 1 1) Si substrates at 1000 °C by separate admittances of trimethylgallium (TMG) and ammonia (NH₃). To achieve high quality GaN films, the optimization in growth temperature and layer thickness of AlN buffer layer between GaN film and Si substrate is required. Cross-sectional transmission electron microscopic observations of the GaN/(1 1 1)Si samples show a nearly parallel orientation relationship between the (0 0 0 1) planes of GaN film and the (1 1 1) planes of Si substrate. Room temperature photoluminescence spectra of high quality GaN films show a strong near band edge emission and a weak yellow luminescence. The achievement of high quality GaN films on (1 1 1) Si substrates is believed to be attributed to enhancement in surface mobilities of the adsorbed surface species and adequate accommodation of lattice mismatch between high temperature AlN buffer layer and Si substrate.     

Self-limiting low-temperature growth of crystalline AlN thin films by plasma-enhanced atomic layer deposition

We report on the self-limiting growth and characterization of aluminum nitride (AlN) thin films. AlN films were deposited by plasma-enhanced atomic layer deposition on various substrates using trimethylaluminum (TMA) and ammonia (NH₃). At 185 °C, deposition rate saturated for TMA and NH₃ doses starting from 0.05 and 40 s, respectively. Saturative surface reactions between TMA and NH₃ resulted in a constant growth rate of ~ 0.86 Å/cycle from 100 to 200 °C. Within this temperature range, film thickness increased linearly with the number of deposition cycles. At higher temperatures (≥ 225 °C) deposition rate increased with temperature. Chemical composition and bonding states of the films deposited at 185 °C were investigated by X-ray photoelectron spectroscopy. High resolution Al 2p and N 1s spectra confirmed the presence of AlN with peaks located at 73.02 and 396.07 eV, respectively. Films deposited at 185 °C were polycrystalline with a hexagonal wurtzite structure regardless of the substrate selection as determined by grazing incidence X-ray diffraction. High-resolution transmission electron microscopy images of the AlN thin films deposited on Si (100) and glass substrates revealed a microstructure consisting of nanometer sized crystallites. Films exhibited an optical band edge at ~ 5.8 eV and an optical transmittance of > 95% in the visible region of the spectrum.     

Graphoepitaxy of High‐Quality GaN Layers on Graphene/6H–SiC

The implementation of graphene layers in gallium nitride (GaN) heterostructure growth can solve self‐heating problems in nitride‐based high‐power electronic and light‐emitting optoelectronic devices. In the present study, high‐quality GaN layers are grown on patterned graphene layers and 6H–SiC by metalorganic chemical vapor deposition. A periodic pattern of graphene layers is fabricated on 6H–SiC by using polymethyl methacrylate deposition and electron beam lithography, followed by etching using an Ar/O₂ gas atmosphere. Prior to GaN growth, an AlN buffer layer and an Al_0.2Ga_0.8N transition layer are deposited. The atomic structures of the interfaces between the 6H–SiC and graphene, as well as between the graphene and AlN, are studied using scanning transmission electron microscopy. Phase separation of the Al_0.2Ga_0.8N transition layer into an AlN and GaN superlattice is observed. Above the continuous graphene layers, polycrystalline defective GaN is rapidly overgrown by better quality single‐crystalline GaN from the etched regions. The lateral overgrowth of GaN results in the presence of a low density of dislocations (≈10⁹ cm⁻²) and inversion domains and the formation of a smooth GaN surface.     

Al预沉积层对金属有机物化学气相沉积方法在Si衬底上生长AlN缓冲层和GaN外延层的影响

采用金属有机物化学气相沉积法(MOCVD)在硅(Si)衬底制备铝/氮化铝/氮化镓(Al/AlN/GaN)多层薄膜,使用光学显微镜(OM)、原子力显微镜(AFM)、X射线衍射(XRD)等手段表征AlN和GaN薄膜的微观结构和晶体质量,研究了TMAl流量对AlN薄膜和GaN薄膜的形核和生长机制的影响。结果表明,预沉积Al层能促进AlN的形核和生长,进而提高GaN外延层的薄膜质量。TMAl流量太低则预沉积Al层不充分,AlN缓冲层的质量取决于由形核长大的高结晶度AlN薄膜与在气氛中团聚长大并沉积的低结晶度AlN薄膜之间的竞争,AlN薄膜的质量随着TMAl流量的升高而提高,GaN薄膜的质量也随之提高。TMAl流量太高则预沉积Al层过厚,AlN缓冲层的质量取决于由形核长大的高结晶度AlN薄膜与Al-Si回融蚀刻之间的竞争,AlN薄膜的质量随着TMAl流量的升高而降低,GaN薄膜的质量也随之降低。     

Sequential structural characterization of layers in the GaN/AlN/SiC/Si(111) system by X-ray diffraction upon every growth stage

X-ray diffraction and transmission electron microscopy techniques have been used to study the dynamics of variation of the structural characteristics and deformation state in SiC, AlN, and GaN epilayers sequentially grown on a Si(111) substrate. In this system, the SiC layer has been grown by solid-phase epitaxy, while the AlN and GaN layers have been deposited by chloride-hydride vapor-phase epitaxy (HVPE) using argon as a carrier gas.     

Synthesis of c-axis oriented AlN thin films on different substrates: A review

Highly c-axis oriented AlN thin films have been deposited by reactive sputtering on different substrates. The crystallographic properties of layered film structures consisting of a piezoelectric layer, aluminum nitride (AlN), synthesized on a variety of substrates, have been examined. Aluminum nitride thin films have been deposited by reactive pulsed-DC magnetron sputtering using an aluminum target in an Ar/N₂ gas mixture. The influence of the most critical deposition parameters on the AlN thin film crystallography has been investigated by means of X-ray diffraction (XRD) analysis of the rocking curve Full-Width at Half Maximum (FWHM) of the AlN-(0 0 0 2) peak. The relationship between the substrate, the synthesis parameters and the crystallographic orientation of the AlN thin films is discussed. A guide is provided showing how to optimize these conditions to obtain highly c-axis oriented AlN thin films on substrates of different nature.     

Influence of double buffer layers on properties of Ga-polarity GaN films grown by rf-plasma assisted molecular-beam epitaxy

Ga-polarity GaN thin films were grown on sapphire (0001) substrates by rf-plasma assisted molecular beam epitaxy (MBE) using a double buffer layer, which consisted of an intermediate-temperature GaN buffer layer (ITBL) grown at 690 °C and a conventional AlN buffer layer deposited at 740 °C. Raman scattering spectra showed that the E₂ (high) mode of GaN film grown on conventional AlN buffer layer is at about 570 cm⁻¹, and shifts to 568 cm⁻¹ when an ITBL was used. This indicates that the ITBL leads to the relaxation of residual strain in GaN film caused by mismatches in the lattice constants and coefficients of thermal expansion between the GaN epilayer and the sapphire substrate. Compared to the GaN film grown on the conventional AlN buffer layer, the GaN film grown on an ITBL shows higher Hall mobility and substantial reduction in the flicker noise levels with a Hooge parameter of 3.87×10⁻⁴, which is believed to be, to date, the lowest reported for GaN material. These results imply that the quality of Ga-polarity GaN films grown by MBE can be significantly improved by using an ITBL in addition to the conventional low-temperature AlN buffer layer.     

Influence of AlN buffer layer thickness and deposition methods on GaN epitaxial growth

A gallium nitride (GaN) epitaxial layer was grown by metal-organic chemical vapor deposition (MOCVD) on Si (111) substrates with aluminum nitride (AlN) buffer layers at various thicknesses. The AlN buffer layers were deposited by two methods: radio frequency (RF) magnetron sputtering and MOCVD. The effect of the AlN deposition method and layer thickness on the morphological, structural and optical properties of the GaN layers was investigated. Field emission scanning electron microscopy showed that GaN did not coalesce on the sputtered AlN buffer layer. On the other hand, it coalesced with a single domain on the MOCVD-grown AlN buffer layer. Structural and optical analyses indicated that GaN on the MOCVD-grown AlN buffer layer had fewer defects and a better aligned lattice to the a- and c-axes than GaN on the sputtered AlN buffer layer.     

Calculation of residual thermal stress in GaN epitaxial layers grown on technologically important substrates

A detailed investigation of residual thermal stress and misfit strain in GaN epitaxial layers grown on technologically important substrates is performed. The thermal stress is low when GaN is grown on AlN, SiC and Si, and relatively higher when Al₂O₃ substrate is used. The stress is compressive for AlN and Al₂O₃ and tensile for Si and SiC substrates. Residual thermal stress analysis was also performed for three layer heterostructures of GaN/AlN/6H-SiC and GaN/AlN/Al₂O₃. The stress remains the same when a sapphire substrate is used with or without an AlN buffer layer but reduces by an order of magnitude when a 6H-SiC substrate is used with an AlN buffer layer.     

Deposition and characterization of c-axis oriented aluminum nitride films by radio frequency magnetron sputtering without external substrate heating

Aluminum nitride (AlN) films were deposited on a variety of substrates (glass, Si, oxidized Si, Al-SiO₂-Si, Cr-SiO₂-Si, and Au-Cr-SiO₂-Si) by radio frequency (RF) magnetron sputtering using an AlN target. The films were deposited without external substrate heating. The effect of RF power, ambient gas (Ar and Ar-N₂) and sputtering pressure on deposition rate and crystallinity were investigated. The structure and morphology of the films were studied by X-ray diffraction, scanning electron microscopy and atomic force microscopy techniques. These investigations revealed that the AlN films prepared in mixed gas ambient (Ar-N₂) were highly c-axis oriented with moderate surface roughness on all the substrate. A strong IR absorption band was observed around 670 cm^− 1 which confirms the presence of Al-N bond in the film. The dc resistivity of the films was measured to be in the range of 10¹¹ to 10¹² Ω-cm at moderate electric fields. The application of these films in piezoelectric based micro-electro-mechanical systems is discussed.     

Growth of GaN and AlN thin films by laser induced molecular beam epitaxy

Hexagonal GaN and AlN thin films were grown by laser induced molecular beam epitaxy using Al or Ga metal as target material and N₂as nitrogen source. The films were deposited on sapphire (0001) and SiC (0001) substrates. Epitaxial growth of GaN has been achieved at 730°C and 10⁻³ mbar N₂ pressure. The AlN films were polycrystalline with predominant (0001) orientation.     

Growth of 3C-SiC on 150-mm Si(100) substrates by alternating supply epitaxy at 1000 °C

To lower deposition temperature and reduce thermal mismatch induced stress, heteroepitaxial growth of single-crystalline 3C-SiC on 150 mm Si wafers was investigated at 1000 °C using alternating supply epitaxy. The growth was performed in a hot-wall low-pressure chemical vapor deposition reactor, with silane and acetylene being employed as precursors. To avoid contamination of Si substrate, the reactor was filled in with oxygen to grow silicon dioxide, and then this thin oxide layer was etched away by silane, followed by a carbonization step performed at 750 °C before the temperature was ramped up to 1000 °C to start the growth of SiC. Microstructure analyses demonstrated that single-crystalline 3C-SiC is epitaxially grown on Si substrate and the film quality is improved as thickness increases. The growth rate varied from 0.44 to 0.76 ± 0.02 nm/cycle by adjusting the supply volume of SiH₄ and C₂H₂. The thickness nonuniformity across wafer was controlled with ± 1%. For a prime grade 150 mm virgin Si(100) wafer, the bow increased from 2.1 to 3.1 μm after 960 nm SiC film was deposited. The SiC films are naturally n type conductivity as characterized by the hot-probe technique.     

Chloride vapor-phase epitaxy of gallium nitride on silicon: Effect of a silicon carbide interlayer

A new approach is described, according to which the use of a thin silicon carbide (SiC) interlayer ensures the suppression of cracking and the simultaneous release of elastic strain in gallium nitride (GaN) epilayers grown by hydride-chloride vapor-phase epitaxy (HVPE) on 1.5-inch Si(111) substrates. Using this method, 20-μm-thick GaN epilayers have been grown by HVPE on Si substrates with AlN (300 nm) and SiC (100 nm) interlayers. A high quality of the obtained GaN epilayers is confirmed by the photoluminescence spectra, where an exciton band with hv_max = 3.45 eV and a half-width (FWHM) of 68 meV is observed at 77 K, as well as by the X-ray rocking curves exhibiting GaN(0002) reflections with a half-width of ω_? = 600 arc sec.     

Synthesis and characterization of 4H-SiC on C-plane sapphire by C60 and Si molecular beam epitaxy

4H-SiC (silicon carbide) films were grown on (0001) sapphire substrate at rather low temperatures(1000-1100 °C) with relative high deposition rate by using fullerene (C₆₀) and silicon solid sources molecular beam epitaxy with substrate nitridation and aluminum nitride (AlN) buffer layer deposition prior to the SiC deposition. The effects of substrate nitridation and AlN buffer layer to the adhesion of the SiC thin films on sapphire have been studied. X-Ray diffraction, pole figure, atomic force microscope, Fourier transform infrared spectroscopy and photoluminescence were employed for the analysis of composition, orientation of the film and surface morphology. Relative high deposition rate at ∼ 165 nm/h was achieved.     

ZnO/SiC/Si异质结构的特性

用MOCVD方法在p型单晶Si（100）基片上外延SiC层,再用直流溅射在SiC层上生长ZnO薄膜,制备出ZnO／SiC／Si异质结构,用XRD和AFM分析了ZnO／SiC／Si和ZnO／Si异质结构中表层ZnO的结构和形貌的差别,研究了这种异质结构的特性．结果表明,在Si（100）基片上外延生长出的是高取向、高结晶质量的SiC（100）层．这个SiC层缓冲层使在Si基片上外延生长出了高质量ZnO薄膜,因为ZnO与SiC的晶格失配比ZnO与Si的晶格失配更低．     

Structural characterization of GaN epilayers on silicon: Effect of buffer layers

Cross-sections of GaN/AlN/3C-SiC/Si(111) system have been studied by electron microscopy techniques. A nanometer thick buffer layer of silicon carbide on Si(111) substrate was formed using an original solid-phase epitaxy method. The subsequent layers of gallium nitride and aluminum nitride were grown by the method hydride-chloride vapor phase epitaxy. The resulting GaN layers display neither threading dislocations nor cracks on any scale. The main fraction of defects in GaN layers have the form of dislocation pileups that are localized at and oriented parallel to the GaN/AlN interface. The dislocation density in the obtained GaN layers is (1–2) × 10⁹ cm⁻², which corresponds to a minimum level reported in the available literature. The buffer AlN layer contains nanopores, which reduce the level of stresses at the GaN/AlN interface and thus almost completely inhibit the formation of threading dislocations.     

Synthesis of aluminum nitride thin films by filtered arc ion plating deposition

Thin films of aluminum nitride (AlN) were deposited on stainless steel and glass substrates by a modified deposition technique, filtered arc ion plating, at an enhanced deposition rate. X-ray diffraction spectra confirmed the exclusive presence of AlN hexagonal wurtzite phase. Under a mixed gas (Ar + N₂) pressure of 0.90 Pa and a bias voltage of − 400 V, the deposited films exhibited a fairly low surface roughness of 2.23 nm. The thin films were proved higher than 75% transparent in the visible spectral region. The bonding strength between the film and substrate was verified higher than 20 N. Thus high performance of such AlN thin films can be expected in applications.     

Evolution of GaN nanoflowers from AlN–SiO2 grains on a silicon substrate by chemical vapor reaction

Gallium nitride (GaN) nanoflowers were synthesized on a silicon (Si) substrate at growth temperatures of 650 and 600 °C and under HCl:NH₃ flow ratios of 1:20, 1:30, and 1:40 by hydride vapor phase epitaxy. Numerous nanorod and nanoneedle burs were formed within each nanoflower. The nanoflower size increased with increasing NH₃ gas flow rate. The nanoflower formation mechanism is proposed based on cross-sectional scanning electron microscopy images and bright field image of scanning transmission electron microscopy. Nanoflowers were evolved from irregular regions with AlN–SiO₂ grains on a Si substrate, i.e., the roughness of substrate affects nanoflower formation by causing nanoburs to protrude, exposing them to higher gas concentrations.     

Epitaxial silicon carbide on a 6″ silicon wafer

The results of the growth of silicon-carbide films on silicon wafers with a large diameter of 150 mm (6″) by using a new method of solid-phase epitaxy are presented. A SiC film growing on Si wafers was studied by means of spectral ellipsometry, SEM, X-ray diffraction, and Raman scattering. As follows from the studies, SiC layers are epitaxial over the entire surface of a 150-mm wafer. The wafers have no mechanical stresses, are smooth, and do not have bends. The half-width of the X-ray rocking curve (FWHM_ω?θ) of the wafers varies in the range from 0.7° to 0.8° across the thickness layer of 80–100 nm. The wafers are suitable as templates for the growth of SiC, AlN, GaN, ZnO, and other wide-gap semiconductors on its surface using standard CVD, HVPE, and MBE methods.