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Optical anisotropy and surface morphology of InGaAs lattice-mismatched with GaAs(0 0 1)
Toshiharu Morimura,Takahiro Mori,Meoung-Whan Cho,Takashi Hanada,Takafumi Yao 한국물리학회 2004 Current Applied Physics Vol.4 No.6
We investigated surface morphology and optical anisotropy of strained InGaAs lms grown on GaAs(001) substrate usingatomic force microscopy (AFM) and reectance dierence/reectance anisotropy spectroscopy (RDS/RAS). High temperature(HT)-grown samples were found to have a rippled surface structure, however for lms grown using a low temperature (LT) growthtechnique, the surface morphology was signicantly improved, without the ripple structure seen on the HT samples. Furthermore,ex situ RD spectra of LT-grown samples showed notable peaks near the critical energies of band structure originated from bulkelectronic transitions.
Koike, Kayo,Lee, Seogwoo,Cho, Sung Ryong,Park, Jinsub,Lee, Hyojong,Ha, Jun-Seok,Hong, Soon-Ku,Lee, Hyun-Yong,Cho, Meoung-Whan,Yao, Takafumi IEEE 2012 Photonics Technology Letters Vol.24 No.6
<P>Four types of GaN-based light-emitting diodes (LEDs) with V-pits formed in different regions were grown by metal–organic chemical vapor deposition. The position of the V-pits embedded in the layers of the LED structures was controlled by varying the growth temperature. We achieved the highest output power and lowest leakage current values with the LED structures comprising V-pits embedded in active regions and the p-GaN textured surface. The V-pit formation enhances the light output power and reverse voltage values by 1.3 times the values of the conventional LED owing to the enhancement of the light scattering probability and the effective filtering of threading dislocations.</P>
Optical anisotropy of GaNAs grown on GaAs(0 0 1)substrate
Takahiro Mori,Takashi Hanada,Toshiharu Morimura,Meoung-Whan Cho,Takafumi Yao 한국물리학회 2004 Current Applied Physics Vol.4 No.6
In this paper GaNxAs1. x surfaces during growth are observed using reectance dierence or reectance anisotropy spectroscopy(RDS or RAS). The epi-layer was grown by solid-source molecular beam epitaxy (MBE) system with a RF nitrogen prasma source.RD spectra showed broader structure and reduced amplitude compared to those of GaAs surfaces; GaAs(2×4)-like features werestill observed with weak and blue-shifted peaks. In the low growth temperature region, an extra structure was also observed around 3.02 eV. We proposed that GaNxAs1-x surface can be classied into three types of the surface.
박진섭,하준석,홍순구,Seog Woo Lee,Meoung Whan Cho,Takafumi Yao,이해우,이상화,이성근,이효종 대한금속·재료학회 2012 ELECTRONIC MATERIALS LETTERS Vol.8 No.2
We investigated the nucleation and growth behavior of GaN on various powders by hydride vapor phase epitaxy. In relative comparison, the nucleation tendency of GaN on each powder can be summarized as AlN >LaN, TiN, NbN > ZrN > ZrB2 > VN, BeO, indicating that the number of nucleation sites increased from right to left. LaN and NbN have not yet been reported as buffer materials for GaN growth. Of these, NbN is expected to be a good buffer material because the interatomic distance on the NbN (111) plane has only 2% difference from that on the GaN (0001) plane.
Stress dependence on N/Ga ratio in GaN epitaxial films grownon ZnO substrates
Tsutomu Minegishi,Takuma Suzuki,Chihiro Harada,Hiroki Goto,Meoung-Whan Cho,Takafumi Yao 한국물리학회 2004 Current Applied Physics Vol.4 No.6
GaN films were grown on ZnO substrate under various beam equivalent pressure ratios by plasma-assisted molecular beamepitaxy (P-MBE). We theoretically calculated the thermal stress caused by the dierence of thermal expansion coecients betweenGaN and ZnO. The changes of stress and critical thickness were evaluated by measurement of XRD for HT GaN and LT GaNbuer grown under Ga-rich and N-rich conditions. From this study, we observed that GaN grown under Ga-rich condition causesGaN lm to under compressive-stress, while GaN grown under N-rich condition was tensile-stressed. Consequently, interdiusionhas no eect on the variation of the critical thickness.
Relation between interdiffusion and polarity for MBE growth of GaN epilayers on ZnO substrates
Takuma Suzuki,Chihiro Harada,Hiroki Goto,Tsutomu Minegishi,Agus Setiawan,고항주,Meoung-Whan Cho,T.Yao 한국물리학회 2004 Current Applied Physics Vol.4 No.6
We report on GaN growth on Zn-polar ZnO substrates using plasma-assisted molecular-beam epitaxy (P-MBE). Before GaNgrowth, ZnO substrate annealing conditions were optimized. Reection high-energy electron diraction (RHEED) patterns afterlow-temperature GaN buer layer annealing changed from streaky to spotty, suggesting that zinc and oxygen atoms interdiusefrom the ZnO substrate into the GaN epilayer. This interdiusion results in a mix-polar GaN epilayer.
Hiroki Goto,Hisao Makino,Agus Setiawan,Takuma Suzuki,Chihiro Harada,Tsutomu Minegishi,Meoung-Whan Cho,Takafumi Yao 한국물리학회 2004 Current Applied Physics Vol.4 No.6
Optical properties of ZnO thin lms with/without MgO-buer annealing were investigated by low and room temperature photoluminescence measurements. The ZnO lms were grown onc-sapphire substrates by plasma-assisted molecular-beam epitaxy employing a thin MgO-buer layer. Dislocation density of ZnO layer was reduced from 5.3· 109 to 1.9· 109 cm. 2 by annealingMgO-buer prior to the growth of ZnO. The intensity of free exciton emission from the sample with MgO-buer annealing wasalmost twice of that from the sample without annealing, while the deep level emission from the sample with MgO-buer annealingwas about 1/3 of that without annealing. The MgO-buer annealing improves optical quality of overgrown ZnO lms.