• Journal of the Optical Society of Korea
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• v.6 no.2
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• pp.48-54
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• 2002

Experimental study is performed on flashlamp-pumped Ti: sapphire lasers with single, double, and four-partial-ellipse-pump cavities aiming at improving the performance of the lasers. The output energy of 604 mJ per pulse with a width of 25 $\mu$s at a total laser efficiency of 0.13% is achieved in the laser pumped by a light pulse of 45$\mu$s without a fluorescent converter The laser output energy versus its Ti: sappy ire rod length, pumping-light pulse duration, and electrical input energy are discussed with or without using a fluorescent converter. The result shows that much more output energy is obtained il a longer Ti: sapphire-rod laser pumped by a shorter light pulse when its output coupler has an optimized transmittance. In addition, an enhancement of output energy by a factor of 7 is achieved. in the laser using a fluorescent converter LD490.

• Laser Solutions
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• v.8 no.2
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• pp.7-12
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• 2005

The material processing of UV nanosecond pulse laser cannot be avoided the material shape change and contamination caused by interaction of base material and laser beam. Nowadays, ultra short pulse laser shorter than nanosecond pulse duration is used to overcome this problem. The advantages of this laser are no heat transfer, no splashing material, no left material to the adjacent material. Because of these characteristics, it is so suitable for micro material processing. The processing of sapphire wafer was done by UV 355nm, green 532nm, IR 1064nm. X-Y motorized stage is installed to investigate the proper laser beam irradiation speed and cycles. Also, laser beam fluence and peak power are calculated.

• Bulletin of the Korean Chemical Society
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• v.15 no.1
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• pp.28-33
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• 1994

The laser-assisted chemical vapor deposition (LCVD) is described, by which the growth of single-phase GaN epitaxy is achieved at lower temperatures. Trimethylgallium (TMG) and ammonia are used as source gases to deposit the epitaxial films of GaN under the irradiation of ArF excimer laser (193 nm). The as-grown deposits are obtained on c-face sapphire surface near 700$^{\circ}$C, which is substantially reduced, relative to the temperatures in conventional thermolytic processes. To overcome the lattice mismatch between c-face sapphire and GaN ad-layer, aluminum nitride(AlN) is predeposited as buffer layer prior to the deposition of GaN. The gas phase interaction is monitored by means of quadrupole mass analyzer (QMA). The stoichiometric deposition is ascertained by X-ray photoelectron spectroscopy (XPS). The GaN deposits thus obtained are characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM) and van der Pauw method.

• Proceedings of the Optical Society of Korea Conference
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• 2003.07a
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• pp.38-39
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• 2003

전기적 저항이 낮은 투명 박막 물질은 현재 flat panel display, electroluminescent device, thin film transistor, solar cell 등 여러 분야에서 연구되고 있다. 그 중에서도 특히 ZnO：Ga는 현재 많이 쓰이는 ITO보다 화학적, 열적으로 안정한 상태를 보이는 투명 전도 산화막 물질로써 본 연구에서는 분광타원법을 이용하여 ZnO：Ga의 광학적 특성을 분석하였다. 본 연구를 위한 시료는 온도에 따른 ZnO：Ga／Sapphire 박막, $O_2$의 압력에 따른 ZnO：Ga／Sapphire 박막, Ga의 doping 농도에 따른 ZnO：Ga／Sapphire 박막으로 제작하였으며, 위상변조형 분광타원계(spectroscopic Phase Modulated Ellipsometer, Jobin-Yvon, UVISEL)를 사용하여 측정대역을 0.74 ~ 4.5 eV, 입사각을 70$^{\circ}$로 하여 측정하였다. (중략)

• Journal of the Korean Vacuum Society
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• v.7 no.s1
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• pp.78-84
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• 1998

Niobium ions of 380 keV energy have been implanted at 300k in sapphire with a dose of $5\times10^{16}\textrm{ions/cm}^2$ and subsequently thermal annealed up to $1100^{\circ}C$ at reducing atmosphere. The behavior of the radiation damage produced by ion implantation followed by annealing is investigated using optical absorption technique and X-ray photoelectron spectroscopy(XPS). It is found that different defects annealed are dependent on the annealing temperature owing to different mechanisms which are proposed on the basis of the optical absorption measurement, and the implanted niobium in sapphire is in different local environments with different charge states after annealing, which are analyzed by XPS measurements.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.23 no.6
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• pp.272-278
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• 2013

In this study, a c-axis displacement and an internal stress of the sapphire crystal of 300 mm length have been analyzed numerically and the crystal length having no sub-grain defects have been predicted. The hot zone structures were modified with the crucible geometry change and the additional insulation layer installed above the crucible. The simulation results show that the c-axis displacement difference between the original hot zone and others originated from the sub-grain defect formations in the sapphire ingot. When the crystal grown by CZ (Czochralski) grower using the modified hot zone, the crystal length having no sub-grain defects was increased about 57 mm maximum than the original one. When the simulation results compared with the experimental one, the predicted crystal length having no sub-grain defects were well corresponded with the experiment one in c-axis wafer of the 300 mm sapphire ingot. Therefore the sapphire crystal of 250 mm length having no sub-grain defects was successfully grown by CZ process.

• Applied Microscopy
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• v.30 no.4
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• pp.337-345
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• 2000

Introduction of the buffer layer and the nitridation of a sapphire substrate were one of the most general methods employed for the reduction of lattice defects in GaN thin films Brown on sapphire by MOCVD. In an effort to improve the initial nucleation and growth condition of the GaN, reactive ion beam (RIB) of nitrogen treatment of the sapphire surface has been attempted. The 10 nm thick, amorphous $AlO_xN_y$ layer was formed by RIB and was partially crystallized alter the main growth of GaN at high temperature, leaving isolated amorphous regions at the interface. The beneficial effect of amorphous layer at interface in relieving the thermal stress between substrate and GaN film was examined by measuring the lattice strain value of the GaN film grown with and without the RIB treatment. Higher order Laue zone pattern (HOLZ) of $[\bar{2}201]$ zone axis was compared with simulated patterns and lattice strain was estimated It was confirmed that the great reduction of thermal strain was achieved by RIB process and the amount of thermal stress was 6 times higher in the GaN film grown by conventional method without the RIB treatment.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.173-173
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• 2010

Recently, a patterned sapphire substrate (PSS) has been intensively used as one of the effective ways to reduce the dislocation density for the III-nitride epitaxial layers aiming for the application of high-performance, especially high-brightness, light-emitting diodes (LEDs). In this paper, we analyze the growth kinetics of the atoms and crystalline quality for the undopped-GaN depending on the facets of the pattern fabricated on a sapphire substrate. The effects of the PSS on the device characteristics of InGaN/GaN LEDs were also investigated. Several GaN samples were grown on the PSS under the different growth conditions. And the undoped-GaN layer was grown on a planar sapphire substrate as a reference. For the (002) plane of the undoped-GaN layer, as an example, the line-width broadening of the x-ray diffraction (XRD) spectrum on a planar sapphire substrate is 216.0 arcsec which is significantly narrower than that of 277.2 arcsec for the PSS. However, the line-width broadening for the (102) plane on the planar sapphire substrate (363.6 arcsec) is larger than that for the PSS (309.6 arcsec). Even though the growth parameters such as growth temperature, growth time, and pressure were systematically changed, this kind of trend in the line-width broadening of XRD spectrum was similar. The emission wavelength of the undoped-GaN layer on the PSS was red-shifted by 5.7 nm from that of the conventional LEDs (364.1 nm) under the same growth conditions. In addition, the intensity for the GaN layer on the PSS was three times larger than that of the planar case. The spatial variation in the emission wavelength of the undoped-GaN layer on the PSS was statistically ${\pm}0.5\;nm$ obtained from the photoluminescence mapping results throughout the whole wafer. These results will be discussed in terms of the mixed dislocation depending on the facets and the period of the patterns.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2012.05a
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• pp.145-146
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• 2012

• Proceedings of the Optical Society of Korea Conference
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• 2009.02a
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• pp.137-138
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• 2009