• 한국재료학회지
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• 제15권5호
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• pp.348-352
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• 2005

Gallium oxyhydroxide (GaOOH) powders were heat-treated in a flowing ammonia gas to form GaN, and the reaction kinetics of the oxide to nitride was quantitatively determined by X-ray diffraction analysis. GaOOH turned into intermediate mixed phases of $\alpha-\;and\;\beta-Ga_2O_3$, and then single phase of GaN. The reaction time for full conversion $(t_c)$ decreased as the temperature increased. There were two-types of rapid reaction processes with the reaction temperature in the initial stage of nitridation at below $t_c$, and a relatively slow processes followed over $t_c$ does not depends on temperatures. The nitridation process was found to be limited by the rate of an interfacial reaction with the reaction order n value of 1 at $800^{\circ}C$ and by the diffusion-limited reaction with the n of 2 at above $1000^{\circ}C$, respectively, at below $t_c$. The activation energy for the reaction was calculated to be 1.84 eV in the temperature of below $830^{\circ}C$, and decreased to 0.38 eV above $830^{\circ}C$. From the comparative analysis of data, it strongly suggest the rate-controlling step changed from chemical reaction to mass transport above $830^{\circ}C$.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1996년도 추계학술대회 논문집
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• pp.33-36
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• 1996

AIN thin films were prepared using by Rf sputtering method on the GaAs(170) substrate and investigated by X-ray diffractometer, IR spectroscopy, n&k system. The parameters were the substrate temperature, RF power, sputtering duration and the $N_2$/Ar ratio. The AlN thin films of (101) orientation were obtained under the conditions of room temperature and the nitrogen of 60 vol.%. The crystallinity of the films, which were grown respectively under the different conditions, were determined by the comparison of the band width of an E$_1$[TO:680$cm^{-1}$ /] phonon mode. The thicknesses of AlN films were decreased dramatically in the region of the nitrogen of 40~60 vol.% according to the increment of the $N_2$/Ar ratio by which the sputter yield got lower.

• Journal of Advanced Marine Engineering and Technology
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• 제29권7호
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• pp.795-800
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• 2005

The optical properties of $ZnS_{y}Se_{1-x-y}:Te_x\;(x\;<\;0.08,\;y\∼0.11$) alloys grown by molecular beam epitaxy (MBE) have been investigated by photoluminescence (PL) and PL-excitation (PLE) spectroscopy. Good optical properties and high crystal quality were established with lattice match condition to GaAs substrate. At room temperature, emission in the visible spectrum region from blue to green was obtained by varying the Te content of the ZnSSe:Te alloy. The efficient blue and green emission were assigned to $Te_{1}$Tel and $Te_{n}$ (n$\geq$2) cluster bound excitons, respectively. Bright blue (462 nm) and green (535 nm) light emitting diodes (LEDs) have been developed using ZnSSe:Te system as an active layer.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2003년도 하계종합학술대회 논문집 II
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• pp.759-762
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• 2003

The epitaxially grown Mg-doped GaN thin film was prepared by MOCVD (Metal Organic Chemical Vapor Deposition) for a SAW(Surface Acoustic Wave) filter. Mg-doped GaN thin film had enough properties for a SAW filter which include crystallinity and morphology. The surface morphology and crystalline of the Mg-doped GaN thin films were characterized using AFM and an X-ray rocking curve. The SAW filter, which was fabricated by lift-off process and frequency response, was measured by HP 8753C network analyzer. Center frequency was 96.687 MHz and SAW velocity was 5801 m/s when wavelength(λ) was 60${\mu}{\textrm}{m}$. Insertion loss was over -10 dB, Q was factor over 200, and side lobe attenuation was over 22 dB which was suitable for use as a SAW filter. Electro-mechanical coupling coefficient (k$^2$) was calculated from the measured data. k$^2$ was from 1 % to 1.44 %. The fabricated SAW filter using Mg-doped GaN/sapphire structure has good qualities as a filter and will be used as a SAW filter for operating RF frequency.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.128.2-128.2
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• 2014

Long-wave infrared detectors using the type-II InAs/GaSb strained superlattice (T2SL) material system with the nBn structure were designed and fabricated. The band gap energy of the T2SL material was calculated as a function of the thickness of the InAs and GaSb layers by the Kronig-Penney model. Growth of the barrier material (Al0.2Ga0.8Sb) incorporated Te doping to reduce the dark current. The full width at half maximum (FWHM) of the 1st satellite superlattice peak from the X-ray diffraction was around 45 arc sec. The cutoff wavelength of the fabricated device was ${\sim}10.2{\mu}m$ (0.12eV) at 80 K while under an applied bias of -1.4V. The measured activation energy of the device was ~0.128 eV. The dark current density was shown to be $1.2{\times}10^{-5}A/cm^2$ at 80 K and with a bias -1.4 V. The responsivity was 1.9 A/W at $7.5{\mu}m$ at 80K and with a bias of -1.9V.

• JSTS:Journal of Semiconductor Technology and Science
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• 제3권1호
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• pp.27-32
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• 2003

Highly reproducible side-wall process for the fabrication of the fine gate length as small as 40nm was developed. This process was utilized to fabricate 40nm InGaAs HEMTs with the 65% strained channel. With the usage of the dual $SiO_2$ and $SiN_x$ dielectric layers and the proper selection of the etching gas, the final gate length (Lg) was insensitive to the process conditions such as the dielectric over-etching time. From the microwave measurement up to 40GHz, extrapolated fT and fmax as high as 371 and 345 GHz were obtained, respectively. We believe that the developed side-wall process would be directly applicable to finer gate fabrication, if the initial line length is lessened below the l00nm range.

• 한국재료학회지
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• 제8권7호
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• pp.591-595
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• 1998

이 연구에서는 HVPE법으로 두께가 350$\mu\textrm{m}$, 면적이 100$\textrm{mm}^2$인 크랙이 없는 freestanding GaN 단결정 기판을 제작하고, 그 특성을 조사하였다. 제작된 GaN 기판의 격자상수는 $c_{o}$ =5.18486$\AA$이었고, 이중 X-선 회절피크의 반치폭은 650 arcsec 이었다. 10K의 온도에서 측정한 PL 스펙트럼은 에너지 밴드 갭 부근에서 중성 도너와 중성 억셉터에 구속된 여기자 및 자유여기자의 소멸에 의한 발광과 결정 결함고 관계하는 깊은 준위에 의한 1.8eV 부근 발광으로 구성되었다. 또한 라만 E2(high)모드 주파수는 567cm-1로서 벌크 GaN 단결정의 값과 같았다. 한편, GaN 기판의 전기저항도형은 n형이었고, 전기 비저항은 0.02$\Omega$.cm이었으며, 캐리어 이동도와 농도는 각각 283$\textrm{cm}^2$/V.s와 1.1$\times$$10^{18}$$cm^{-3}$이었다.

• 한국결정성장학회지
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• 제21권5호
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• pp.187-192
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• 2011

비극성 a-GaN의 성장 시 기판의 경사각은 GaN epi의 품질을 결정하는 중요한 변수로서 양질의 a-GaN 성장을 위해서는 R-면 기판의 경사각이 정밀하게 제어된 기판이 요구된다. 본 연구에서는 R-면 기판의 경사각 ${\alpha}$와 ${\beta}$의 목표값이 각각 0, -0.1, -0.15, -0.2, -0.4, $-0.6^{\circ}$와 -0.1, 0, $0.1^{\circ}$인 절단기판을 제조하였다. 절단기판의 경사각을 x-ray를 이용하여 측정하고 통계적인 분석을 통해 기판의 경사각 제어공정에 대한 신뢰성을 평가하였으며, R-면 기판의 경사각의 공차는 ${\pm}0.03^{\circ}$의 값을 가졌다. R-면 기판은 상대적으로 큰 이방성에 의해 c-면 기판에 비해 휨(BOW)과 두께편차(TTV)가 상대적으로 큰 분포를 갖는 것으로 나타났다. AFM을 이용하여 기판 표면을 관찰한 결과, 측정된 R-면기판의 step 높이는 0.2~0.4 nm로 거의 일정한 값을 가졌으며 step 너비는 경사각 ${\alpha}$가 증가함에 따라 156 nm에서 26 nm로 감소하였으며 이와같은 R-면 기판의 step 구조의 변화는 epi 성장에 큰 영향을 미치는 것으로 판단된다.

• ETRI Journal
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• 제11권4호
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• pp.67-74
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• 1989

n-GaAs/A1GaAs계의 화합물 반도체 접합에 형성되는 이차원 전자 가스를 캐패시턴스-전압(C-V), 각도 의존 자기저항(SdH), 전자 빔 반사(EBER)등의 측정 방법을 통하여 A1GaAs 조성비(x)는 0.281, 전도대와 가전도대의 밴드 불연속은 각각 밴드 갭($E_g$)의 69%와 31%임을 알았고, 여기에 존재하는 이차원 전자가스의 면농도는 $5.4\times10^11cm^-2, 페르미 준위 $E_F$는 25mev임을 알았다. 또한 도핑 된 A1GaAs층에서 흔히 나타나는 Franz-Keldysh진동은 불순물의 활성화도가 작으면 형성되는 전기장의 약화로 나타나지 않는다는 것을 발견하였다.

• Current Photovoltaic Research
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• 제4권3호
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• pp.108-113
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• 2016

III-V compound semiconductor based thin film solar cells promise relatively higher power conversion efficiencies and better device reliability. In general, the thin film III-V solar cells are fabricated by an epitaxial lift-off process, which requires an $Al_xGa_{1-x}As$ ($x{\geq}0.8$) sacrificial layer and an inverted solar cell structure. However, the device performance of the inversely grown solar cell could be degraded due to the different internal diffusion conditions. In this study, InGaP/GaAs double-junction solar cells are inversely grown by MOCVD on GaAs (100) substrates. The thickness of the GaAs base layer is reduced to minimize the thermal budget during the growth. A wide band gap p-AlGaAs/n-InGaP tunnel junction structure is employed to connect the two subcells with minimal electrical loss. The solar cell structures are transferred on to thin metal films formed by Au electroplating. An AlAs layer with a thickness of 20 nm is used as a sacrificial layer, which is removed by a HF:Acetone (1:1) solution during the epitaxial lift-off process. As a result, the flexible InGaP/GaAs solar cell was fabricated successfully with an efficiency of 27.79% under AM1.5G illumination. The efficiency was kept at almost the same value after bending tests of 1,000 cycles with a radius of curvature of 10 mm.