Papers by Keyword: HVPE

Abstract: During crystal growth processes, growth sectors are formed due to growth along different crystallographic directions. Although the crystal structure in the different growth sectors is unchanged, strain induced topography contrast is observed by synchrotron X-ray topography. In this study, synchrotron monochromatic beam X-ray topography (SMBXT), synchrotron X-ray plane wave topography (SXPWT), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and secondary ion mass spectrometry (SIMS) are used to characterize growth sectors in gallium nitride (GaN) substrate wafers grown by patterned hydride vapor phase epitaxy (HVPE). The SMBXT images reveal the boundaries of {0001} and {1122} type growth sectors. Strain maps generated from SXPWT shows that the out-of-plane strains in different growth sectors have a difference of the order of 10^-5. SEM images from SE2 signal shows no contrast of growth sector boundaries while images from Robinson detector (RBSD) show different growth sectors as different grey scale contrast, indicating a strain effect. SIMS analysis shows that the different oxygen impurity levels in the growth sectors, which is the origin of the strain. A formation mechanism of growth sectors in patterned HVPE grown GaN wafers is proposed.

Abstract: Schottky-barrier diodes with a diameter of ~10 μm are fabricated on n-GaN epitaxial films grown by hydride vapor-phase epitaxy (HVPE) on sapphire substrates. The changes in the parameters of the diodes under irradiation with 15 MeV protons are studied. The carrier rate was found to be 130-145 cm^-1. The linear nature of the dependence N = F (D) (N is carrier concentration, and D, the irradiation dose) shows that compensation of the material is associated with transition of electrons from shallow donors to deep acceptor levels which are related to primary radiation defects.

Abstract: GaN epitaxial layers were successfully grown by hydride vapour phase epitaxy (HVPE) on β-Ga₂O₃ substrates produced by cleaving. The initial stages of GaN epitaxial growth on β-Ga₂O₃ were studied by scanning electron microscopy (SEM) and x-ray diffraction analysis (XRD). The nucleation and the transition from the nucleation layer to a continuous GaN film were studied. It was found that the growth starts with formation of small crystallites on the substrate surface. As the growth continues, crystallites transform into pyramidal islands which increase in size and merge together. It was found that the structural quality of the GaN layers rapidly improves with increasing thickness. The full width at half maximum of x-ray ω rocking curves for (0002) peak decreased from 1370 to 540 arcsec as the deposition time was increased from 30 to 120 sec. This corresponds to the variation of the nominal layer thickness from 250 nm to 1000 nm.

Abstract: A method to grow gallium nitride (GaN) films directly on the graphene layers by hydride vapor phase epitaxy (HVPE) method is reported in this work. We used a chemical vapor deposition (CVD) method to grow graphene on a copper foil, and the test results showed the presence of monolayer graphene at most regions. GaN films were grown on the graphene/MO-GaN substrate (GaN which was grown by metal organic vapor phase deposition) and MO-GaN template by HVPE method. Raman Spectroscopy, Scanning Electron Microscopy (SEM), and X-Ray Diffraction (XRD) were adopted for characterization. By comparing with the MO-GaN substrate, the crystalline quality of the GaN films were both increased. However, the crystalline quality of the HVPE-GaN with graphene interlayer is slightly lower than that directly grown on MO-GaN.

Abstract: Thick GaN films grown with different V/III ratio on sapphire by hydride vapour phase epitaxy have been investigated. The V/III ratio is changed from 240 to 30. All the GaN films, which are n type, show only (0002) oriented peak and have the band emission with no yellow luminescence bands. When V/III ratio is 30, the full width at half maximum of (0002) X-ray rocking curve is the smallest, line-width of the band edge emission is narrow, the surface morphology shows step-flow growth and the growth rate is the highest.

Abstract: The paper reports the setting up of a model of fluid dynamic for GaN HVPE system and the simulation. The deposition of GaN with the variation of the gas flow inlet velocities is investigated. The influence of diffusion coefficient on the deposition of GaN is also discussed. It is found that the influence of the gas flow inlet velocities on the deposition is large and the influence of diffusion coefficient on the deposition of GaN is small in vertical HVPE.

Abstract: The investigated AlGaN epitaxial layers were grown by hydride vapor phase epitaxy (HVPE) on a commercial P+ SiC substrate or on an N+ SiC Lely substrate with a p+ SiC layer previously grown by sublimation epitaxy. To investigate the electrical characteristics of the n-p heterojunction, mesa structures of 100, 200 and 1500 microns in diameter were fabricated by reactive ion etching. Investigation of electrical characteristics shows good quality of grown n- AlGaN/p-SiC heterojunctions. This shows applicability of this technological combination for producing n-AlGaN/p-SiC bipolar or FET transistors.

Abstract: We have investigated deep trap concentrations in hydride vapor pressure epitaxy (HVPE) - grown GaN by measuring three-dimensional carrier concentration profiles and ionization energies. Schottky contacts were fabricated on 28-68μm thick films using Ni/Au contacts. Extensive capacitance-voltage measurements were made in the temperature range 100-350K at reverse bias voltages in the range 0 to –5V. Effective carrier concentrations and ionization energies were determined from three-dimensional plots of concentration-temperature-depth. Carrier concentration versus temperature plots show slowly changing three-step behavior. During the first step, all the plots rise linearly up to about 200K reaching respective plateaus before reversing courses downwards again linearly. Ionization energy plots, on the other hand, are almost linear all the way up to 350 K showing some tendency of upward bending. Trap concentrations were determined from carrier concentrations and previously measured deep level transient spectroscopy (DLTS) plots as function of reverse bias voltages. In almost every case, trap concentrations also rise linearly with increasing depth in the samples.

Abstract: GaN films are grown on Si(111) with low-temperature GaN (LT-GaN) layers as buffer layers by hydride vapor phase epitaxy (HVPE). The LT-GaN layers are deposited at different temperatures ranging from 400 to 900 °C. The surface property, the structure and optical properties of the GaN films with different LT-GaN layers are studied. When deposition temperature of LT-GaN layer is 600 °C, the GaN film shows the best properties.