Nucleation and epitaxial growth of ZnO on GaN(0001) (original) (raw)
Related papers
Journal of Crystal Growth, 2015
Plasma-assisted molecular beam epitaxy was used to grow ZnO(0001) layers on GaN(0001)/4H-SiC buffer layers deposited in the same growth chamber equipped with both N-and O-plasma sources. The GaN buffer layers were grown immediately before initiating the growth of ZnO. Using a substrate temperature of 445 1C and an O 2 flow rate of 2.5 standard cubic centimeters per minute, we obtained ZnO layers with statistically smooth surfaces having a root-mean-square roughness of 0.3 nm and a peak-to-valley distance of 3 nm as revealed by atomic force microscopy. The full-width-at-halfmaximum for x-ray rocking curves obtained across the ZnO(0002) and ZnO(10 1 5) reflections was 198 and 948 arcsec, respectively. These values indicated that the mosaicity of the ZnO layer was comparable to the corresponding values of the underlying GaN buffer layer. Reciprocal space maps showed that the in-plane relaxation of the GaN and ZnO layers was 82% and 73%, respectively, and that the relaxation occurred abruptly during the growth. Room-temperature Hall-effect measurements revealed that the layers were inherently n-type and had an electron concentration of 1 Â 10 19 cm À 3 and a Hall mobility of 51 cm 2 /V s.
MRS Internet Journal of Nitride Semiconductor Research
The nature and impact of ZnO buffer layers on the initial stages of the hydride vapor phase epitaxy (HVPE) of GaN have been studied by x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), x-ray diffraction (XRD) and photoluminescence (PL). During pre-growth heating, the surface ZnO layer was found to both desorb from ZnO-coated sapphire and react with the underlying sapphire surface forming a thin ZnAl2O4 alloy layer between ZnO and sapphire surface. This ZnO-derived surface promotes the initial nucleation of the GaN and markedly improves material surface morphology, quality and growth reproducibility.
LP-MOCVD growth of GaN on silicon substrates—comparison between AlAs and ZnO nucleation layers
Materials Science and Engineering: B, 1999
The impact of AlAs and ZnO nucleation layers on the low-pressure MOCVD growth of GaN on silicon substrates is the subject of this study. In both cases, prior to the high-temperature deposition of the GaN main layer a thin low-temperature GaN buffer layer has been found to improve the crystal quality. Especially in the case of a ZnO nucleation layer, no single crystalline growth of GaN was obtained without a low-temperature GaN buffer layer. Furthermore, the crystallographic quality of the GaN layer is strongly dependent on the strength of the (0001) texture of the ZnO grains. The ZnO (0001)-texture is independent of the Si(111) or Si(001) orientation and allows for single crystalline growth of GaN on both types of Si surfaces. TEM investigations show, that the ZnO nucleation layer has completely vanished after the epitaxial process. In contrast, AlAs nucleation layers remain stable as proven by X-ray diffraction and TEM measurements.
Thin Solid Films, 2010
Thick, epitaxial ZnO thin films have been grown on (0001) GaN buffered Al 2 O 3 substrates using an aqueous solution at 90°C. Films with improved structural, optical and electrical characteristics, were grown using a lateral epitaxial overgrowth (LEO) method. Different photoresist masks were used to enable LEO. The masks included linear windows and two different hexagonal arrays of circular windows. Films that exceeded a critical thickness mechanically failed through buckling, consistent with the large compressive stresses expected due to the mismatch of the ZnO lattice with the underlying GaN substrate. It was shown that improved mechanical stability could be achieved using the LEO method. Without LEO, a film thickness no greater than 4 µm could be grown without buckling. The critical thickness could be increased to 10 µm using linear windows, whereas a critical thickness of 50 μm was achieved with one array of circular windows, and 80 µm for a second array. The two different arrays of circular windows differed relative to their orientation on the substrate. It was also shown that the critical thickness increased with increasing distance between the growth windows. Optical transmission, micro-photoluminescence and Hall Effect measurements showed that the LEO method also results in improved optoelectronic properties.
Japanese Journal of Applied Physics, 2006
We have found that the surfaces of ZnO(000 1 1) annealed in a box made of ceramic ZnO exhibit atomically flat stepped and terraced structures. Structural and optical properties of ZnO are also improved by this annealing technique. Full width at half maximum of X-ray rocking curves of the ZnO substrates were decreased and green photoluminescence caused by defects were eliminated by the annealing. We have also found that epitaxial growth of GaN on atomically flat ZnO(000 1 1) substrates at room temperature proceeds in a layer-by-layer mode, while growth on the as-received substrates results in formation of amorphous materials. These results indicate that the use of the annealing technique improves, not only crystal quality of ZnO substrates, but also morphology of the GaN films grown on them.
Growth of GaN on porous SiC and GaN substrates
Journal of Electronic Materials, 2003
We have studied the growth of GaN on porous SiC and GaN substrates, employing both plasma-assisted molecular beam epitaxy (PAMBE) and metalorganic chemical vapor deposition (MOCVD). For growth on porous SiC, transmission electron microscopy (TEM) observations indicate that the epitaxial GaN growth initiates primarily from surface areas between pores, and the exposed surface pores tend to extend into GaN as open tubes and trap Ga droplets. The dislocation density in the GaN layers is similar to, or slightly less than, that observed in layers grown on non-porous substrates. For the case of GaN growth on porous GaN the overgrown layer replicates the underlying dislocation structure (although considerable dislocation reduction can occur as this overgrowth proceeds, independent of the presence of the porous layer). The GaN layers grown on a porous SiC substrate were found to be mechanically more relaxed than those grown on non-porous substrates; electron diffraction patterns indicate that the former are free of misfit strain or are even in tension after cooling to room temperature. Significant changes in the stress of the overgrown layers on porous GaN were also found, as seen in line shifts of low-temperature photoluminescence spectra.
Journal of Crystal Growth, 2010
A new hydride vapor phase epitaxy (HVPE)-based approach for the fabrication of freestanding GaN (FS-GaN) substrates was investigated. For the direct formation of low-temperature GaN (LT-GaN) layers, the growth parameters were optimized: the polarity of ZnO, the growth temperature, and the V/III ratio. The FS-GaN layer was achieved by gas etching in an HVPE reactor. A fingerprint of Zn out-diffusion was detected in the photoluminescence measurements, especially for the thin (80 mm) FS-GaN film; however, a thicker film (400 mm) was effectively reduced by optimization of GaN growth.
MOCVD of ZnO thin films for potential use as compliant layers for GaN on Si
Journal of Crystal Growth, 2008
This paper explores the use of nanostructured zinc oxide (ZnO) films as a compliant buffer layer for the growth of gallium nitride (GaN) on silicon substrates. Thin films of ZnO have been deposited on silicon (1 1 1) substrates by liquid injection metalorganic chemical vapour deposition (MOCVD) using dimethyl zinc-tetrahydrofuran adduct and oxygen. The use of the adduct complex avoids prereaction between the dialkyl zinc complex and oxygen which has been observed elsewhere. ZnO films deposited by this method were stoichiometric and of high purity, with no detectable carbon contamination. Films were deposited over a temperature range 350-550 1C, and exhibited a nanowire-like morphology. Subsequent deposition of GaN layers grown by molecular beam epitaxy (MBE) on the ZnO film resulted in the transformation of the nanowires to gallium oxide, accompanied by virtually complete removal of zinc from the layer. A heteroepitaxially oriented (c-axis) GaN/gallium oxide/silicon structure was produced after the nitride deposition which consisted of characteristic columnar GaN with the GaN[0 0 0 1]||Si [1 1 1]. Selective area electron diffraction of the by-product oxide interlayer showed a polycrystalline-like behaviour that gave rise to a random azimuthal distribution of the GaN grains. r
Growth of GaN on SiC substrates by MBE
We report the growth of Al x Ga 1-x N alloys on (0001) sapphire by the method of Electron Cyclotron Resonance-assisted Molecular Beam Epitaxy (ECR-MBE). The films were doped n-type with silicon at carrier concentration levels from 10 16 to 10 19 cm -3 . SEM studies reveal smooth surface morphology consistent with the observed 3x4 surface reconstruction in the RHEED pattern. Independent determination of the Al-concentration and the lattice constant of the alloys shows that Vegard's rule is obeyed in the pseudo-binary GaN-AlN system. The bandgap of the alloys, determined by transmission and photoluminescence measurements, was found to depend linearly on Al-concentration.