• Journal of the Korean Crystal Growth and Crystal Technology
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• v.34 no.4
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• pp.139-142
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• 2024

Along with the use of wide bandgap energy materials such as SiC and GaN in power semiconductors and the development trend of devices, many research results have been reported, including the success of research on AlN single crystals with higher energy gaps and the development of 2-inch single crystal wafers. However, AlN single crystals grown using chemical vapor deposition have been developed into thin films less than a few micrometers thick, but there are almost no results with thicknesses greater than that. Therefore, in this study, we attempted to grow by applying HVPE (Hydride vapor phase epitaxy), one of the chemical vapor deposition methods. The grown AlN single crystal was manufactured using self-designed equipment, and we attempted to establish the conditions for manufacturing AlN single crystals on sapphire wafer. We would like to characterize the growth behavior through an optical microscope observation.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.11a
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• pp.170-170
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• 2003

We have implanted on sapphire substrate with various ions and investigated the properties of GaN epilayers grown on implanted sapphire substrate by metal organic chemical vapor deposition (MOCVD). Sapphire is typical substrate for GaN epilayers. However, there are many problems such as lattice mismatch and thermal coefficient difference between sapphire substrate and GaN. The ion implanted substrate's surface had decreased internal tree energies during the growth of the GaN epilayer, md the misfit strain was relieved through the formation of an AlN phase on the ions implanted sapphire(0001) substrates. [1] The crystal and optical properties of GaN epilayer grown in ions implanted sapphire(0001) substrate were improved.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.38 no.10
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• pp.671-677
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• 2001

A RuO$_2$ Schottky photo-detector was designed and fabricated with GaN layers on the sapphire substrate. For good absorption of UV light, an epitaxial structure with undoped GaN(0.5 ${\mu}{\textrm}{m}$)/n￣-GaN(0.1${\mu}{\textrm}{m}$)/n＋-GaN(1.5${\mu}{\textrm}{m}$) was grown by MOCVD. The structure had the carrier concentrations of 3.8$\times$10$^{18}$ cm￣$^3$, the mobility of 283$\textrm{cm}^2$/V.s. After ECR etching process for mesa structure with the diameter of about 500${\mu}{\textrm}{m}$, Al ohmic contact was formed on GaN layer. After proper passivation between the contacts with Si$_3$/N$_4$, was formed on undoped GaN layer. The fabricated Schottky diode had a specific contact resistance of 1.15$\times$10$^{-5}$ ［$\Omega$.$\textrm{cm}^2$］. It has a low leakage current of 305 pA at -5 V, which was attributed by stable characteristics of RuO$_2$ Schottky contact. In optical measurement, it showed the high UV to visible extinction ratio of 10$^{5}$ and very high responsivity of 0.23 A/W at the wavelength of 365nm.

• Korean Journal of Materials Research
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• v.14 no.7
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• pp.494-499
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• 2004

The structural, electrical and optical properties of GaN epilayers grown on various ion-implanted sapphire(0001) substrates by MOCVD were investigated. Sapphire substrates have been widely adopted to grow high quality GaN epilayer despite the large differences of lattice constant and thermal expansion coefficient between them. So, GaN or AlN buffer layer and pre-treatment was indispensably introduced before the GaN epilayer growth. The ion-implanted substrate's surface had decreased internal free energies during the growth of the ions implanted sapphire(0001) substrates. The crystal and optical properties of GaN epilayers grown in ions implanted sapphire(0001) substrate were improved. Also, excessively roughened and modified surface by ions degraded the GaN epilyers. Not only the ionic radius but also the chemical species of implanted sapphire(0001) substrates could improve the properties of GaN epilayers grown by MOCVD. This result implies that higher quality of GaN epilayers was achieved by using ion-implanted sapphire(0001) substrate with various ions.

• JSTS:Journal of Semiconductor Technology and Science
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• v.14 no.5
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• pp.682-687
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• 2014

We have performed reverse gate bias stress tests on AlGaN/GaN-on-Si Heterostructure FETs (HFETs). The shift of threshold voltage ($V_{th}$) and the reduction of on-current were observed from the stressed devices. These changes of the device parameters were not permanent. We investigated the temporary behavior of the stressed devices by analyzing the temperature dependence of the instabilities and TCAD simulation. As the baseline temperature of the electrical stress tests increased, the changes of the $V_{th}$ and the on-current were decreased. The on-current reduction was caused by the positive shift of the $V_{th}$ and the increased resistance of the gate-to-source and the gate-to-drain access region. Our experimental results suggest that electron-trapping effect into the shallow traps in devices is the main cause of observed instabilities.

• ETRI Journal
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• v.38 no.5
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• pp.972-980
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• 2016

An ultra-wideband microwave monolithic integrated circuit high-power amplifier with excellent input and output return losses for phased array jammer applications was designed and fabricated using commercial $0.25-{\mu}m$ AlGaN/GaN technology. To improve the wideband performance, resistive matching and a shunt feedback circuit are employed. The input and output return losses were improved through a balanced design using Lange-couplers. This three-stage amplifier can achieve an average saturated output power of 15 W, and power added efficiency of 10% to 28%, in a continuous wave operation over a frequency range of 6 GHz to 18 GHz. The input and output return losses were demonstrated to be lower than -15 dB over a wide frequency range.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.205-205
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• 2013

테라헤르쯔(terahertz: THz)파는 0.1~10 THz 의 범위로 적외선과 방송파 사이에 광대역 주파수 스펙트럼을 차지하고 있으며 직진성, 투과성, 그리고 낮은 에너지 (meV)를 가지고 있어 비 파괴적이고 무해한 장점을 지니고 있다. Ti:sapphire laser와 같은 femto-pulse source 등이 많은 발전이 되어 현재 많은 연구와 발전이 이루어지고 있다. femto-pulse source를 이용한 THz 응용에서는 높은 저항, 큰 전자 이동도, 그리고 아주 짧은 전하수명의 기판을 요구하는데 저온에서 성장한 (low-temperature grown : LT) GaAs는 격자 내에 Gallium 자리에 Arsenic이 치환 하면서 AsGa antisite가 발생하여 전하수명을 짧아지는 것을 응용하여 가장 많이 이용되고 있다. 현재 THz 응용분야에서 보다 작고 가격경쟁력이 있는 광통신을 이용한 THz photomixer등이 활발히 연구 하고 있다. 광섬유 내에서 손실과 분산이 최소값을 가지는 부분이 1.55 ${\mu}m$ 부근이고 In0.53Ga0.47As 기판을 이용하였을 때 여기에 완벽하게 만족하게 된다. 하지만 LT-InGaAs 의 경우 AsGa antisite로 인하여 carrier lifetime은 짧아지지만 높은 n-type 전하밀도를 가지게 된다. 이때 Be을 doping하여 전하밀도를 보상하여 높은 저항을 유지해야 하는데 Be의 활성화를 위해서는 열처리를 필요로 한다. 하지만 열처리를 하면 carrier lifetime이 길어지기 때문에 carrier lifetime과 저항을 적절히 조율해야 한다. 이는 물질자체의 특성이기 때문에 InGaAs는 GaAs보다 낮은 amplitude와 짧은 cut-off frequency를 가진다. 본 연구에서는 보다 높은 저항을 얻기 위하여 molecular beam epitaxy를 이용하여 semi-insulating InP:Fe 기판위에 격자 정합된 InGaAs:Be/InAlAs multi quantum well (MQW)를 온도별 ($250{\sim}400^{\circ}C$), 주기별 (50~150)로 성장을 하였고 이때 InGaAs layer의 Be doping level은 $2{\times}1018\;cm^{-3}$, Ex-situ annealing은 $550^{\circ}C$에서 10분으로 고정 하였다. THz 발생 실험에서는 InGaAs/InAlAs MQW은 4000 pA로 1,000 pA를 가지는 InGaAs epilayer보다 4배 높은 전류 신호를 얻을 수 있었고 모든 샘플이 2 THz에서 cut-off frequency를 가지고 있었다. THz 검출 실험에서는 LT-InGaAs:Be epilayer LT-InGaAs:Be/InAlAs, HT-InGaAs/InAlAs 샘플이 각각 180, 9000, 12000 pA의 전류신호를 가지고 있었고 모든 샘플이 2 THz에서 cut-off frequency를 가지고 있었다. HT-InGaAs/InAlAs MQW를 이용한 검출실험에서는 InGaAs layer가 defect free이지만 LT-InGaAs:Be/ InAlAs MQW 보다 높은 전류 신호를 얻을 수 있었다. 이는 InAlAs layer가 저항만 높이는 것뿐만 아니라 carrier trapping layer로써의 역할도 하는 것으로 사료된다.

• Proceedings of the Optical Society of Korea Conference
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• 2005.02a
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• pp.156-157
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• 2005

Monte Carlo photon simulation 기법을 사용하여 광추출효율 관점에서 InGaN LED를 분석하였다. InGaN/sapphire 칩의 경우, AlInGaP나 InGaN/SiC 칩에서와는 달리, 칩의 측벽면을 기울여 주는데서 오는 광추출효율 개선 효과는 매우 미미하였다. 이는 InGaN/sapphire 칩의 경우 사파이어 기판의 굴절률 상대적으로 작아서 활성층으로부터 생성된 광자들의 상당량이 기판으로 넘어갈 때 전반사현상으로 말미암아 기판으로 넘어가지 못하고 상대적으로 두께가 매우 얇은 에피택시 층에 갇히기 때문으로 파악되었다. 이와 같은 효과는 epitaxial side down mount의 광추출효율이 크게 개선되지 못하는 원인으로도 작용하게 되는데, epitaxial side down mount의 잠재력을 살릴 수 있는 방안의 하나는 texture된 기판위에 결정층을 성장시키는 것이라고 할 수 있다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.8
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• pp.677-681
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• 2009

$In_xGa_{1-x}N$ alloys with 20-nm-thickness were deposited onto Mg:GaN/AlN/SiC substrates by MOCVD at $800\;^{\circ}C$. TMGa, TMIn and $NH_3$ were used as the precursor of gallium, indium and nitrogen, respectively. The mole ratio of indium in $In_xGa_{1-x}N$ films varied between 0 and 0.2. The energy-band-gaps of the films were obtained from the photoluminescence and cathodoluminescence peaks. The mole ratios of $In_xGa_{1-x}N$ films were calculated by applying Vegard's law to XRD results. The energy-band-gap versus indium composition plot for $In_xGa_{1-x}N$ alloys were well fit with a bowing parameter of 2.27.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.6
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• pp.553-557
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• 1999

In order to investigate the optical properties of the $Al_XGa_{1-X}N/GaN$ thin film grown by metalorganic chemical vapor deposition (MOCVD) method, the photoluminescene (PL), photocurrent (PC) and persistent photoconductivity (PPC) measurements were carried out at room temperature. The band gap of the $A1_x$$Ga_{1-x}$N/GaN was determined to 3.70 eV by the PL and PC measurements. The PC measurement on the light illumination from the top of the $A1_x$$Ga_{1-x}$N/GaN thin film provides peaks at 3.70, 3.43, and around 2.2 eV. The PC spectrum by the illumination passing through from the substrate of the sample can be shown at 3.43 eV together with a broad tail band from the GaN band edge to around 2.23 eV. The photocurrent quenching and anomalous PPC decay observed in PPC measurements indicate that metastable electron states are fomed in the band gap of GaN layer to trap electrons which can be tunneled the potential barrier for long recovery time.