• Journal of the Korean Crystal Growth and Crystal Technology
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• v.13 no.5
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• pp.235-240
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• 2003

The development of large area GaN substrates is one of important issues in expanding of GaN-based applications. In order to investigate the possibility, GaN thick films were grown by a sublimation technique, using MOCVD-GaN films grown on a sapphire as a seed-crystal substrate and a commercial GaN powder as a source material. The pressure in chamber under the fixed flow rate of $N_2$ gas and $NH_3$ gas was kept at 1 atmosphere and the effects of the various processing parameters such as the distance between source material and seed crystal, the temperature of top- and bottom heater and the growth time during the growth of GaN thick film were investigated. The growth feature and microstructure of the GaN thick films were observed by SEM and XRD. The optical bandgap properties and the defects were evaluated by the PL measurement. By these results, the growth conditions such as the distance between the GaN source and the seed substrate, the growth temperature and the growth time were determined for the satisfied growth of GaN thick films.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.121-121
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• 1999

Gallium nitride (GaN) semiconductor is intensively under investigation for commercialization of short wavelength light emitting devices and laser diodes. One of serious obstacles to overcome is to reduce the defect density in GaN film grown by various techniques such as MOCVD, HVPE, etc. Many research groups including SAIT are trying to improve the defect density to 106-107/cm2 from the level of 108-1010/cm2. We have investigated epitaxial growth behaviour of GaN thin and thick films under hidride vapour phase epitaxy (HVPE) condition. In this report, we present the microstructural and crystallographical characteristics of the GaN films grown on sapphire (0001) substrate which were studied by both conventional and high-resolution transmission electron microscopy (TEM). Also we present some microscopic analysis results obtained from GaN films grown by ELO(dpitzsial lateral overgrowth)-HVPE and from GaN quantum well structures grown by MOCVD. Another serious problem in growing GaN thick film by HVPE is internal micro-cracks. We also comment the origin of the micro-crack.

• Proceedings of the Materials Research Society of Korea Conference
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• 2001.05a
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• pp.106-106
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• 2001

• Korean Journal of Materials Research
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• v.10 no.3
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• pp.241-245
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• 2000

Thick GaN films were grown on (0001) sapphire substrates using the direct reaction gallium and ammonia. The GaN films grew dominantly along [0002] direction, but included the growth of GaN(1010) planeq with V-shaped facetted surfaces at low temperature. With increasing growth temperature, however, the growth of GaN (1010) and (1011) planes was appeared from the films, which gives rise to the growth of hexagonal crystal with pyramid-shaped surface. The growth rate of GaN films increased with increasing growth temperature, but decreased at $1270^{\circ}C$ because the GaN films began to decompose into Ga and N at the temperature. It seemed that the crystal and optical qualities of the GaN films improve with increasing $NH_3$ flow rate. From X-ray diffraction (XRD) and photoluminescence (PL) measurements, it was observed that the yellow luminescence (YL) appeared to be significant as the peak intensity of (1010) plane of XRD spectra increased.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1996.11a
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• pp.37-39
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• 1996

A hydride vapor phase epitaxy (HVPE) method was performed to prepare the GaN thick-films on c-plane sapphire substrates. The full-width at half maximum of double crystal X-ray rocking curve from 350${\mu}{\textrm}{m}$ thick GaN was 576 arcsecond. The photo- luminescence spectrum measured (at room temperature) show the narrow bound exciton(I$_2$) line and weak donor-acceptor pair recombination peak, however, there was not observed deep donor-acceptor pare recombination indicate the GaN crystals prepared in this study are of high purity and high crystalline quality.

• Korean Journal of Materials Research
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• v.8 no.6
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• pp.526-531
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• 1998

A hydride vapor phase epitaxy (HVPE) method was performed to grow the $10~240\mu{m}$ thick GaN films on (111) spinel $MgAl_2O_4$ substrate. The GaN films on $MgAl_2O_4$ substrate revealed a photoluminescence (PL) characteristics of the impurity doped GaN by the out-diffusion and auto-doping of Mg from $MgAl_2O_4$ substrate during GaN growth. The PL spectrum measured at 10K consists of free and bound excitons related recombination transitions and impurity-related donor-acceptor pair recombination and its phonon replicas. However, the deep-level related yellow band emission was not observed. The peak energy of neutral donor bound excitonic emission and the frequency of Raman $E_2$ mode were exponentially decreased with increasing the GaN thicknesses. and the frequency of E, Raman mode was shifted with the relation of $\Delta$$\omega$=3.93$\sigma$($cm^{-1}$/GPa), where l1 (GPa) is the residual strain in the GaN epilayers.

• Korean Journal of Materials Research
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• v.23 no.3
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• pp.161-167
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• 2013

The ZnO thin films were grown on GaN template substrates by RF magnetron sputtering at different RF powers and n-ZnO/p-GaN heterojunction LEDs were fabricated to investigate the effect of the RF power on the characteristics of the n-ZnO/p-GaN LEDs. For the growth of the ZnO thin films, the substrate temperature was kept constant at $200^{\circ}C$ and the RF power was varied within the range of 200 to 500W at different growth times to deposit films of 100 nm thick. The electrical, optical and structural properties of ZnO thin films were investigated by ellipsometry, X-ray diffraction (XRD), atomic force microscopy (AFM), photoluminescence (PL) and by assessing the Hall effect. The characteristics of the n-ZnO/p-GaN LEDs were evaluated by current-voltage (I-V) and electroluminescence (EL) measurements. ZnO thin films were grown with a preferred c-axis orientation along the (0002) plane. The XRD peaks shifted to low angles and the surface roughness became non-uniform with an increase in the RF power. Also, the PL emission peak was red-shifted. The carrier density and the mobility decreased with the RF power. For the n-ZnO/p-GaN LED, the forward current at 20 V decreased and the threshold voltage increased with the RF power. The EL emission peak was observed at approximately 435 nm and the luminescence intensity decreased. Consequently, the crystallinity of the ZnO thin films grown with RF sputtering powers were improved. However, excess Zn affected the structural, electrical and optical properties of the ZnO thin films when the optimal RF power was exceeded. This excess RF power will degrade the characteristics of light emitting devices.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.3
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• pp.387-387
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• 1998

This paper reports on a thermodynamic analysis for the GaN thick film growth by vapor phaseepitaxy method. The thermodynamic calculation was performed using a chemical stoichiometric algorism. Thesimulation variables include the growth temperature in a range 400~1500 K, the gas ratios $(GaCl_3)/(GaCl_3+NH_3)$and $(N_2)/(GaCl_3+NH_3)$. The theoretical calculation predicts that the growth temperature of GaN be in thelower range of 450~750 K than the experimental results. The difference in the growth temperature betweenthe simulation and the experiments indicates that the vapor phase epitaxy of GaN is kinetically limited,presumably, due to the high activation energy of thin film growth.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.3
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• pp.388-395
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• 1998

This paper reports on a thermodynamic analysis for the GaN thick film growth by vapor phase epitaxy method. The thermodynamic calculation was performed using a chemical stoichiometric algorism. The simulation variables include the growth temperature in a range 400~1500 K, the gas ratios $(GaCl_3)/(GaCl_3+NH_3)$ and $(N_2)/(GaCl_3+NH_3)$. The theoretical calculation predicts that the growth temperature of GaN be in the lower range of 450~750 K than the experimental results. The difference in the growth temperature between the simulation and the experiments indicates that the vapor phase epitaxy of GaN is kinetically limited, presumably, due to the high activation energy of thin film growth.

• Proceedings of the KIEE Conference
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• 1999.07d
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• pp.1910-1912
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• 1999

This paper was described electrical characteristics of Metal/GaN contact for application of GaN thin films. The lowest contact resistivity was $1.7\times10^{-7}[\Omega-cm^2]$ at Ti/Al Structure. Mean while, GaN MESFETs have been fabricated with a 250 nm thick channel on a high resistivity GaN layer grown by GAIVBE system. For a gate-source diode reverse bias of 35 V, the gate leakage current was $120{\mu}A$. From the data, we estimate the transconductance for our GaN MESFET to be 25 mS/mm.