• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.10
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• pp.784-789
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• 1998

In this work, the optical properties of freestanding GaN single crystalline substrate grown by hydride vapor phase epitaxy(HVPE) were investigated. The low temperature PL spectrum in freestanding GaN consists of free and bound exciton emissions, and a deep DAP recombination around at 1.8eV. The optically-pumped stimulated emission in freestanding GaN substrate was observed at room temperature. At the maximum power density of 2MW/$\textrm{cm}^2$, the peak energy and FEHM of stimulated emission were 3.318 eV and 8meV, respectively. The excitation power dependence on the integrated emission intensity indicates the threshold pumping power density of 0.4 MW/$\textrm{cm}^2$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.06a
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• pp.67-70
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• 1998

In this work, the freestanding GaN single crystalline substrates without cracks were grown by hydride vapor phase epitaxy (HVPE). The GaN substrates, having a current maximum size of 350 $\mu\textrm{m}$-thickness and 10${\times}$10 $\textrm{mm}^2$ area, were obtained by HVPE growth GaN on sapphire substrate and subsequent mechanical removal of the sapphire substrate. A lattice constant of c$\_$0/=5.18486 ${\AA}$ and a FWHM of DCXRD was 650 arcsec for the single crystalline freestanding GaN substrate. The low temperature PL spectrum consist of excitonic emission and deep donor to acceptor pair recombination at 1.8 eV. The Raman E$_2$ (high) mode frequency was 567 cm$\^$-1/ which was the same as that of strain free bulk single crystals. The Hall mobility and carrier concentration was 283 $\textrm{cm}^2$/V$.$sec and 1.1${\times}$10$\^$18/ cm$\^$-3/, respectively. The freestanding and crack-free GaN single crystalline substrate suitable for the homoepitaxial growth of GaN, and the HVPE method are promising approaches for the preparation of large area, crack-free GaN substrates.

• Korean Journal of Materials Research
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• v.8 no.7
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• pp.591-595
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• 1998

In this work, the freestanding GaN single crystalline substrates without cracks were grown by hydride vapor phase epitaxy (HVPE) and its some properties were investigated. The GaN substrate, having a current maximum size of 350 $\mu\textrm{m}$-thickness and 100$\textrm{mm}^2$ area, were obtained by HVPE growth of thick film GaN on sapphire substrate and subsequent mechanical removal of the sapphire substrate. A lattice constant of $C_o$= 5.18486 $\AA$ and a FWHM of DCXRD was 650 arcsec for the single crystalline GaN substrate. The low temperature PL spectrum consist of three excitonic emission and a deep D- A pair recombination at 1.8eV. The Raman E, (high) mode frequency was 567$cm^{-1}$ which was the same as that of strain free bulk single crystals. The Hall mobility and carrier concentration was 283$cm^3$<\ulcornerTEX>/ V.sand 1.1$\times$$10^{18}cm^{-3}$, respectively.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.11 no.3
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• pp.106-111
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• 2001

The freestanding GaN substrates were grown by hydride vapor phase epitaxy (HVPE) on (0001) sapphire substrate and prepared by using laser induced lift-off. After a mechanical polishing on both Ga and N-surfaces of GaN films with 100$\mu\textrm{m}$ thick, their polarities have been investigated by using chemical etching in phosphoric acid solution, 3 dimensional surface profiler and Auger electron spectroscopy (AES). The composition of the GaN film measured by AES indicted that Ga and N terminated surfaces have the different N/Ga peak ratio of 0.74 and 0.97, respectively. Ga-face and N-face of GaN revealed quite different chemical properties: the polar surfaces corresponding to (0001) plane are resistant to a phosphoric acid etching whereas N-polar surfaces corresponding to(0001) are chemically active.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.7
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• pp.427-431
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• 2017

In this paper, we discuss ${\beta}-Ga_2O_3$ thin films that have been grown on freestanding GaN (FS-GaN) using furnace oxidation. A GaN template was grown by horizontalhydride vapor phase epitaxy (HVPE), and FS-GaN was fabricated using the laser lift off (LLO) system. To obtain ${\beta}-Ga_2O_3$ thin film, FS-GaN was oxidized at $900{\sim}1,100^{\circ}C$. Surface and cross-section of prepared ${\beta}-Ga_2O_3$ thin films were observed by field emission scanning electron microscopy (FE-SEM). The single crystal FS-GaNs were changed to poly-crystal ${\beta}-Ga_2O_3$. The oxidized ${\beta}-Ga_2O_3$ thin film at $1,100^{\circ}C$ was peel off from FS-GaN. Next, oxidation of FS-GaNwas investigated for 0.5~12 hours with variation of the oxidation time. The thicknesses of ${\beta}-Ga_2O_3$ thin films were measured from 100 nm to 1,200 nm. Moreover, the 2-theta XRD result indicated that (-201), (-402), and (-603) peaks were confirmed. The intensity of peaks was increased with increased oxidation time. The ${\beta}-Ga_2O_3$ thin film was generated to oxidize FS-GaN.

• Proceedings of the Optical Society of Korea Conference
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• 2005.07a
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• pp.212-213
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• 2005

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.12
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• pp.776-780
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• 2015

In this paper, we have studied the effect of mechanical polishing to Ga-polar face for reducing the wafer bowing and strain in free-standing GaN. After the mechanical polishing to Ga-polar face, the bowing of the free-standing GaN substrate significantly decreased with increasing the size of diamond slurry, and eventually changed the bowing direction from concave to convex. Furthermore, the full width at half maximum (FWHM) of high-resolution X-ray diffraction (HR-XRD) were decreased, especially the FWHM of (1 0 2) reflection for $1.0{\mu}m$ size of diamond slurry was significantly decreased from 630 to 203 arcsec. In the case, we confirmed that the compressive strain in Ga-polar face was fully released by Raman measurement.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.11
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• pp.702-706
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• 2016

We demonstrated that self-separation FS-GaN (freestanding-GaN) was grown on MELO (maskless epitaxially lateral overgrowth) GaN template by horizontal HVPE (hydride vapor phase epitaxy). Before thick GaN grwoth, MELO GaN template was grown on patterned GaN template by MOCVD (metal organic chemical vapor deposition). The laterally overgrown GaN would consist of a continuous well coalesced layer. The mixed TDD (threading dislocation density) of seed and wing region were $8{\times}10^8cm^{-2}$ and $7{\times}10^7cm^{-2}$, respectively. After thick GaN grown by HVPE, the self-separation between thick GaN and sapphire substrate was generated at seed region. The regions of self-separation for FS-GaN and sapphire were observed by FE-SEM. Moreover, Raman results indicated that the compressive strain of seed and wing regions at FS-GaN substrate were slightly released compared to that of thick GaN grown on conventional GaN template. The optical properties of the FS-GaN substrate were examined by using PL (photoluminescence). The PL exhibited that donor bound exciton and donor acceptor pair were observed at low temperature. The effects on optical and structural properties of FS-GaN substrate have been discussed in detail.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.9
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• pp.32-37
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• 2008

Freestanding hydride vapor phase epitaxy grown GaN(Gallium Nitride) substrates subjected to various polishing methods were characterized for their surface and subsurface conditions, Although CMP(Chemical Mechanical Polishing) is one of the best approaches for reducing scratches and subsurface damages, the removal rate of Ga-polar surface in CMP is insignificant($0.1{\sim}0.3{\mu}m$/hr) as compared with that of N-polar surface, Therefore, conventional MP(Mechanical Polishing) is commonly used in the GaN substrate fabrication process, MP of (0001) surface of GaN has been demonstrated using diamond slurries with different abrasive sizes, Diamond abrasives of size ranging from 30nm to 100nm were dispersed in ethylene glycol solutions and mineral oil solutions, respectively. Significant change in the surface roughness ($R_a$ 0.15nm) and scratch-free surface were obtained by diamond slurry of 30nm in mean abrasive size dispersed in mineral oil solutions. However, MP process introduced subsurface damages confirmed by TEM (Transmission Electronic Microscope) and PL(Photo-Luminescence) analysis.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.175-175
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• 2010

이전 연구에서는 사파이어 기판 위에 이종에피성장 방법으로 성장한 높은 인듐 조성의 극박 InGaN/GaN 다층 양자우물 구조를 이용한 근 자외선 (near-UV) 영역의 광원에 대하여 보고하였다. 본 연구에서는 HVPE (Hydride Vapor Phase Epitaxy) 법을 이용하여 성장된 free-standing GaN 기판 위에 유기금속 화학증착법 (MOCVD) 을 이용하여 GaN 동종에피박막과 높은 인듐 조성의 InGaN/GaN 다층 양자우물을 성장하였고 그 특성을 분석하였다. Free-standing GaN 기판은 표면 조도가 0.2 nm 인 평탄한 표면을 가지며 $10^7/cm^2$ 이하의 낮은 관통전위밀도를 가진다. Freestanding GaN 기판 위에 성장 온도와 V/III 비율을 조절하여 GaN 동종에피박막을 성장하였다. 또한 100 nm 두께의 동종 GaN 박막을 성장한 후에 활성층으로 이용될 높은 인듐 조성의 InGaN/GaN 다층 양자우물구조를 성장하였다. Free-standing GaN 기판 위에 성장된 GaN 동종에피박막과 다층 양자우물구조의 표면 형상은 주사 탐침 현미경 (scanning probe microscopy, SPM) 을 이용하여 관찰하였고 photoluminescence (PL) 측정과 cathodoluminescence (CL) 측정을 통하여 광학적 특성을 확인하였다. 사파이어 기판 위에 성장된 2 um 의 GaN을 이용하여 성장된 높은 인듐 조성의 InGaN/GaN 다층 양자우물의 결함밀도는 $2.5 \times 10^9/cm^2$ 이지만 동일한 다층 양자우물구조가 free-standing GaN 기판 위에 성장되었을 경우 결함 밀도는 $2.5\;{\times}\;10^8/cm^2$로 감소하였다. Free-standing GaN 기판의 관통전위 밀도가 $10^7/cm^2$ 이하로 낮기 때문에 free-standing GaN 기판에 성장된 높은 인듐 조성의 다층 양자우물구조의 결함밀도가 GaN/sapphire 에 성장된 다층 양자우물의 결함밀도 보다 감소했음을 알 수 있다. Free-standing GaN 기판에 성장된 다층 양자 우물은 성장온도에 따라 380 nm 에서 420 nm 영역의 발광을 보이며 PL 강도도 GaN/sapphire 에 성장한 다층 양자우물의 PL 강도 보다 높은 것을 확인할 수 있다. 이것은 free-standing GaN 기판에 성장된 높은 인듐 조성의 InGaN/GaN 다층 양자우물구조의 낮은 결함밀도로 인하여 활성층의 발광 효율이 개선된 것임을 보여준다.