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T. Minegishi,Z. Vashaei,G. Fujimoto,H. Suzuki,K. Sumitani,M. Cho,M. Suemitsu,O. Sakata,S. Tokairin,T. Yao,Y. Narita 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.3
We studied ZnO growth on 3C-SiC(001)/Si(001) templates. In-situ reflection high- energy electron diffraction (RHEED) observations implied that ZnO grown on 3C-SiC(001) had a critical thickness (50 nm). From a structural characterization by using X-ray diffraction, we revealed that ZnO films thinner than the critical thickness grown on 3C-SiC(001) had a [10-11] orientation with 4-fold in-plane symmetry. On the other hand, ZnO films thicker than the critical thickness consisted of [10-11] and [0001] orientations. Also, the portion of [0001] oriented ZnO increased with the layer thickness. Possible interface configurations of ZnO(10-11)/3C-SiC(001) and ZnO(0001)/ZnO(10-11) are suggested.
C.Harada,H.Makino,H.Goto,T.Minegishi,T.Suzuki,M.W.Cho,T.Yao 한국물리학회 2004 Current Applied Physics Vol.4 No.6
We report on a surface property of bulk ZnO crystals and an optical method to evaluate it. Bulk ZnO crystals have a damagedsurface layer due to chemomechanical polishing. We prepared the ZnO crystals by etching, and evaluated the improvement of thesurface by high-resolution X-ray diraction (XRD) and photoluminescence (PL). In PL measurements, the relative intensity of therst order longitudinal optical phonon replica of free exciton (FX-1LO) to second order process (FX-2LO) was compared. Therelative intensity becomes weak with increasing etched depth and nally saturates at the etched depth of 5l m. This result agrees wellwith XRD results.
Roles of Kinetics and Energetics in the Growth of AlN by Plasma-Assisted Molecular Beam Epitaxy
I. H. Im,D. C. Oh,J. H. Chang,M. W. Cho,S. W. Lee,T. Yao,T. Minegishi,T. Hanada 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.3
The roles of kinetics and energetics in the growth processes of AlN on c-sapphire by plasmaassisted molecular beam epitaxy are investigated by varying the growth rate from 1 to 31 °A/min and the substrate temperature from 800 to 1000 C. The energetics is found to govern the growth of AlN in the low-growth rate region even at a low substrate temperature of 800 C owing to the enhanced residence time of adatoms, thereby increasing the surface migration length. As the growth rate increases, the growth tends to be governed by kinetics because of a reduction in the residence time of adatoms. Consequently, the surface roughness and crystal quality are greatly improved for the low-growth-rate case. In addition, the lattice strain relaxation is completed from the beginning of epitaxy for energetics-limiting growth while lattice strain relaxation is retarded for kinetics-limiting growth because of pre-existing partial strain relaxation. Energetics becomes more favorable as the substrate temperature is raised because of an increase in the surface diusion length owing to an enhanced diusion coecient. Consequently high-crystal-quality AlN layers are grown under the energetics-limiting growth condition with a screw dislocation density of 7.4 × 108 cm−2 even for a thin 42-nm thick film.
Structural Properties of CrN Buffers for GaN Growth
W. H. Lee,오동철,한창석,이현용,I. H. Im,J. J. Kim,K. Sumitani,구경완,M. W. Cho,O. Sakata,조성준,홍순구,S. T. Kim,T. Minegishi,T. Yao,T.Hanada 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.3
We have investigated the structural properties of CrN layers grown on (0001) Al2O3 substrates by molecular-beam epitaxy. The CrN layers of high-crystal quality are obtained at a low growth temperature of 500 C. X-ray diraction studies indicate that the CrN layers grow along the <111> direction with a cubic structure. In-situ reflection high-energy electron diraction investigations clarify that the CrN layers have the following epitaxy relationship with the Al2O3 substrates: <12- 1> of (111) cubic CrN // <11-20> of (0001) corundum Al2O3 and <101> of (111) cubic CrN // <1-100> of (0001) corundum Al2O3. Based on the above results, the mismatch of the in-plane lattice spacing between the CrN layers and the Al2O3 substrates is evaluated to be around 6.6 %. When the CrN layers are used as the buer layers for GaN growth, the GaN layers grown on the CrN layers show well-resolved excitonic emission lines in the photoluminescence spectra, whereas the GaN layers grown without the CrN layers exhibit a broad near-band-edge emission. It is suggested that CrN buers are eective in relieving the lattice mismatch between Al2O3 substrates and GaN layers.
Growth mechanism of ZnO low-temperature homoepitaxy
S. H. Park,T. Minegishi,H. J. Lee,D. C. Oh,H. J. Ko,J. H. Chang,T. Yao 호서대학교 공업기술연구소 2010 공업기술연구 논문집 Vol.29 No.1
The authors report on the growth mechanism of ZnO films at the low growth temperature of 500 oCusinghomoepitaxy,whosetemperatureisunavailabletoobtainhigh-qualityZnOfilmsinheteroepitaxy. One typical set of ZnO films were grown on (0001) ZnO substrates by molecular-beam epitaxy: a standard structure without buffer and two buffered structures with high-temperature (HT) homobuffer and low-temperature (LT) homobuffer. As a result, the LT homobuffered structure had the outstanding material properties: the surface roughness is 0.9 nm, the full width at half maximum of x-ray rocking curve is 13 arcsec, and the emission linewdith of donor-bound excitons is 2.4 meV. In terms of the theoretical interpretation of the experimentally obtained electron mobilities, it was found that the LT homobuffered structure less suffers from the dislocation scattering and the ionized-impurity scattering, compared to the HT homobuffered structure. It is proposed that in the ZnO low-temperature homoepitaxy, the LT homobuffer plays a key role in suppressing the outdiffusion of contaminants and inducing the complete termination of dislocations in the homointerface, which result in the formation of smooth wetting layer on the homointerface.
Surfactant-Mediated Molecular Beam Epitaxy of ZnO
H. Suzuki,G. Fujimoto,M. W. Cho,T. Yao,T. Minegishi 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.3
We investigated the effects of atomic hydrogen as a surfactant for plasma-assisted molecular beam epitaxial growth of ZnO. Atomic hydrogen was provided by dissociation of hydrogen gas, and ZnO films were grown on Zn-polar ZnO substrates. The growth mode was observed by using reflected high-energy electron diffraction (RHEED) and the presence of atomic hydrogen enhanced two-dimensional growth. Without atomic hydrogen, ZnO homoepitaxial growth directly on ZnO substrate showed a three-dimensional growth mode. Employing a low-temperature ZnO buffer layer (LT-ZnO) enabled a two-dimensional growth mode. However, with atomic hydrogen, twodimensional growth mode was achieved without using LT-ZnO. Low-temperature epitaxial growth was also achieved. Atomic force microscopy (AFM) measurements showed that the surfaces of ZnO films grown with atomic hydrogen were quite smooth. The structural and the optical properties were characterized using high resolution X-ray diffraction and photoluminescence. Theses properties were improved by atomic hydrogen irradiation. Thus, hydrogen acts an effective surfactant to enhance the layer by layer growth mode.