Thick GaN layers on sapphire with various buffer layers (original) (raw)
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Thick GaN films grown on patterned sapphire substrates
ECS Transactions, 2011
GaN thick films, grown on specially patterned 2" sapphire substrates by HVPE methods have lower bowing and are less susceptible to fracture then ones, grown on unpatterned substrates under the same growth conditions. Numerical calculation shows good agreement with experiments. Such substrates could be an alternative to expen-sive GaN wafers sliced from GaN boules.
Characterization of an AlN buffer layer and a thick-GaN layer grown on sapphire substrate by MOCVD
Journal of Materials Science, 2010
An AlN buffer layer and a thick-GaN layer for high-electron-mobility transistors (HEMTs) were grown on sapphire substrate by metal-organic chemical vapor deposition (MOCVD). The structural and morphological properties of the layers were investigated by high resolution X-ray diffraction (HRXRD) and atomic force microscopy (AFM) techniques. The optical quality of the thick-GaN layer was also evaluated in detail by a photoluminescence (PL) measurement. It was found that the AlN buffer layer possesses high crystal quality and an atomically flat surface with a root-mean-square (rms) roughness of 0.16 nm. The screw-and edge-type dislocation densities of the thick-GaN layer were determined as 5.4 9 10 7 and 5.0 9 10 9 cm-2 by means of the mosaic crystal model, respectively. It was observed that the GaN layer has a smooth surface with an rms of 0.84 nm. Furthermore, the dark spot density of the GaN surface was estimated as 6.5 9 10 8 cm-2 over a scan area of 4 lm 2 .
Thick GaN layers grown by hydride vapor-phase epitaxy: hetero- versus homo-epitaxy
Journal of Crystal Growth, 2003
In this paper, an overview will be given of the growth of thick GaN layers by hydride vapor-phase epitaxy. Two different kinds of substrates were used, that is MOCVD-grown GaN templates on sapphire and GaN single crystals. The layers grown on sapphire-based substrates suffer from the problem of cracking and pit formation. Although the morphology is not mirror-like, the optical and electrical quality of the material is excellent as demonstrated by photoluminescence and Hall-Van der Pauw measurements. The layers grown on Ga-polar GaN single crystals have almost perfect morphologies with only a very low density of pits. For the N-polar substrates the morphology is very rough, exhibiting the same features as are observed for the N-face MOCVD-grown GaN layers, both on sapphire and on N-face GaN single crystals. r
The roles of low-temperature buffer layer for thick GaN growth on sapphire
Journal of Crystal Growth, 2008
Thick GaN films were grown on two different low-temperature GaN (LT-GaN)-buffer layers, i.e., one-and two-step LT-GaN buffer, by hydride vapor-phase epitaxy (HVPE). NH 4 Cl layer was included in two-step LT-GaN, which was evaluated by X-ray diffraction patterns. Many voids were observed at the interface for both samples. We will discuss the mechanism of void formation for both samples. The full-width at half-maximum (FWHM) values of (0 0 0 2) o-rocking curves were 390 and 440 arcsec for 200-mm-thick GaN on oneand two-step LT-GaN, respectively. The 200-mm-thick high-temperature GaN (HT-GaN) film on two-step LT-GaN was self-separated without any cracks after cooling down. NH 4 Cl layer included into two-step LT-GaN buffer was effectively contributed to the voids formation and self-separation in realizing a stress-free free-standing GaN (FS-GaN) substrate.
Optimization of GaN nucleation layer deposition conditions on sapphire substrates in HVPE system
Vacuum, 2008
The influence of deposition conditions of nucleation GaN layer on the properties of high-temperature GaN layer, grown on sapphire substrates, was investigated. The hydride vapor phase epitaxy (HVPE) three-section horizontal hot-wall furnace technique was applied. Various temperatures, HCl flows and time intervals of nucleation layer growth were utilized. Based on previous studies the following experimental conditions were selected: temperature was kept at 450 or 570 1C, and HCl flows were 8 or 10 sccm/min. The duration of nucleation layer deposition was 5, 7 and 9 min. The scanning electron microscopy technique was applied for the investigation of nucleation layer morphology after migration. Thick GaN layers were deposited during the three-step growth process at 1060 1C. Samples with various surface morphologies were obtained. Photoluminescence spectra and X-ray measurements were performed, which permitted clarifications of the influence of growth conditions of the nucleation layer on the properties of high-temperature layers. r
Journal of Crystal Growth, 2006
We report the remarkably improved crystal quality of semi-insulating GaN grown by metalorganic chemical vapor deposition on an AlN buffer layer, which is deposited on sapphire substrate. The electrical and structural properties are characterized by dark current-voltage transmission line model and X-ray diffraction measurements. It is found that the crystal quality of the GaN epilayer is strongly related with the growth temperature of the decreased-temperature GaN interlayer. In comparison with the normal GaN grown on sapphire, the crystal quality is remarkably improved along with a semi-insulating electrical character. The high-mobility field effect transistors device based on the semi-insulating GaN shows good pinch off properties. Our electrical measurement results of GaN grown directly on an AlN buffer indicated that the as-grown-undoped GaN is naturally semi-insulating material. The origination of the residual donors in normal GaN grown on sapphire substrate is also discussed.
The growth of thick GaN film on sapphire substrate by using ZnO buffer layer
Journal of Crystal Growth, 1993
Sputtered ZnO layers have been used as buffer layers in the growth of GaN by hydride VPE. With these buffers we have not only improved the reproducibility of the growth of GaN but also achieved the preparation of single crystalline GaN films alone by etching buffer layers away. In this paper we have studied the effects of the ZnO buffer layer on GaN films.
Journal of Crystal Growth, 1998
Microstructures of GaN films grown by low pressure metalorganic vapor-phase epitaxy on (0 1 1 2) sapphire substrates were investigated using transmission electron microscopy. The crystallographic structure of the GaN buffer layer grown at 550°C was uniquely hexagonal. Grain boundaries and stacking faults in the as-grown buffer layer are much less than those in the buffer layer grown on (0 0 0 1) sapphire substrates. Defects in the as-grown epitaxial layers are predominantly edge type dislocations with Burgers vector b" 11 1 0 02. No screw dislocations or domain boundaries in the epilayer were observed in the as-grown samples.
Buffer layers for the growth of GaN on sapphire by molecular beam epitaxy
Journal of Crystal Growth, 1999
The change of structural, optical and electrical properties of GaN grown by plasma assisted molecular beam epitaxy on sapphire due to the introduction of GaN and AlN bu!er layers is investigated. Whereas the layer surface becomes smoother its structural features remain very small. Photoluminescence and resistivity measurements con"rm an increased density of extended defects produced by the bu!er layer. A predominant lateral growth mode as known from metalorganic vapour-phase epitaxy is not observed.
Growth of GaN by metal organic vapor phase epitaxy on ZnO-buffered c-sapphire substrates
Journal of Crystal Growth, 2008
The materials quality and availability of large-area bulk GaN substrates is currently considered a key problem for the continuing development of improved GaN-based devices. Since industrial fabrication of bulk GaN substrates with suitable materials quality has proven very difficult, the opto-GaN industry is currently based on heteroepitaxy using either c-sapphire or 6H SiC substrates. ZnO is promising as a substrate material for GaN because it has the same wurtzite structure and a relatively small lattice mismatch ($1.8%).