• Proceedings of the Optical Society of Korea Conference
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• 2000.08a
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• pp.22-23
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• 2000

GaAs/AlGaAs나 InGaAs/InGaAsP와 같은 반도체 기판을 이용한 전계광학 광변조기는 LD나 SOA와 같은 광소자와 단일기판 집적이 가능하고 낮은 chirping과 높은 변조대역폭을 갖는 외부광변조기로서의 장점으로 인하여 마이크로파 대역의 초고속광통신소자로 각광을 받아왔다. 특히 진행파의 속도가 정합된 traveling-wave 전극 구조를 갖는 경우 변조대역폭은 30-400Hz에 달하고 있다$^{(1)}$ . 그러나 한편으로는 반도체의 전계광학계수(electro-Optic Coefficient)가 LiNbO$_3$에 비해 10분의 1정도로 작아 상대적으로 동작전압이 커지는 단점이 대두되며 실제 구동전압이 수십 V에 이르고 있다. 이런 단점을 극복하기 위하여 p-i-n 구조를 이용하여 전계 집속도를 높이는 방법이 제안되어 동작전압이 2 V/mm 정도까지 감소하였다$^{(2)}$ . 본 논문에서는 이와 같은 반도체 전계광학 광변조기에서의 소신호 및 대신호 광변조특성을 분석함으로써 보다 높은 변조대역폭과 보다 낮은 동작전압을 갖는 구조를 연구하였다. (중략)

• Proceedings of the IEEK Conference
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• 2000.11b
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• pp.17-20
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• 2000

We have enhanced the yield of 0.25 ${\mu}{\textrm}{m}$ T-gate $Al_{0.25}$G $a_{0.75}$As/I $n_{0.2}$G $a_{0.8}$As P-HEMT using three-layer E-beam lithography process and selective etching process. The three-layer resist structure (PMMA/copolymer/ PMMA=2000 $\AA$/3000 $\AA$/2000 $\AA$) and three developers (Benzene：IPA=1：1,Methanol：IPA =1：1,MIBK：IPA=1：3) were used for fabrication of a wide-head T-gate by the conventional double E-beam exposure technology. Also 1 wt% citric acid： $H_2O$$_2$：N $H_{4}$OH(200m1：4ml：2.2ml) solution were used for uniform gate recess. The etching selectivity of GaAs over $Al_{0.25}$G $a_{0.75}$As is measured to be 80. So these P-HEMT processes can be used in X-band MMIC LNA fabrication.ion.ion.ion.

• Proceedings of the Korean Magnestics Society Conference
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• 2008.12a
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• pp.154.2-154.2
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• 2008

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.6
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• pp.372-375
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• 2017

ZnO thin films were deposited by RF magnetron sputtering and then diffused by using an As source in the ampouletube. Also, the ZnO p-n homojunction was made by using As-doped ZnO thin films, and its properties were analyzed. After the As doping, the surface roughness increased, the crystal quality deteriorated, and the full width at half maximum was increased. The As-doped ZnO thin films showed typical p-type properties, and their resistivity was as low as $2.19{\times}10^{-3}{\Omega}cm$, probably because of the in-diffusion from an external As source and out-diffusion from the GaAs substrate. Also, the ZnO p-n junction displayed the typical rectification properties of a p-n junction. Therefore, the As diffusion method is effective for obtaining ZnO films with p-type properties.

• Journal of the Korean Vacuum Society
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• v.18 no.5
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• pp.352-357
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• 2009

The InAs multi-quantum dots (MQDs) solar cell and InGaAs multi-quantum wells (MQWs) solar cell to cover 1.1 eV and 1.3 eV were designed by 1D poisson, respectively. The MQDs and MQWs of 5, 10, 15 layers were grown by molecular beam epitaxy. The photo luminescence results showed that the 5 period stacked MQDs have the highest intensity at around 1.1 eV with 57.6 meV full width at half maximum (FWHM). Also we can observe 10 period stacked MQWs peak position which has highest intensity at 1.31 eV with 12.37 meV FWHM. The density and size of QDs were observed by reflection high energy electron diffraction pattern and atomic force microscope. Futhermore, AlGaAs/GaAs sandwiched tunnel junctions were modified according to the width of GaAs layer on p-type GaAs substrates. The structures with GaAs width of 30 nm and 50 nm have backward diode characteristics. In contrast, tunnel diode characteristics were observed in the 20 nm of that of sample.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.115-115
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• 1999

GaN는 직접천이형 wide band gap(3.4eV) 반도체로서 청색/자외선 발광소자 및 고출력 전자장비등에의 응용성 때문에 폭넓게 연구되고 있다. 이러한 넓은 분야의 응용을 위해서는 열 적으로 안정된 Ohmic contact을 반드시 실현되어야 한다. n-type GaN의 경우에는 GaN계면에서의 N vacancy가 n-type carrier로 작용하기 때문에 Ti, Al, 같은 금속을 접합하여 nitride를 형성함에 의해서 낮은 접촉저항을 갖는 Ohmic contact을 하기가 쉽다. 그러나 p-type의 경우에는 일 함수가 크고 n-type와 다르게 nitride가 형성되지 않는 금속이 Ohmic contact을 할 가능성이 많다. 시료는 HF(HF:H2O=1:1)에서 10분간 초음파 세척을 한 후 깨끗한 물에 충분히 헹구었다. 그런 후에 고순도 Ar 가스로 건조시켰다. Pd와 Ni은 열적 증착법(thermal evaporation)을 사용하여 p-GaN에 상온에서 증착하였다. 현 연구에서는 열처리에 의한 Pd의 clustering을 줄이기 위해서 wetting이 좋은 Ni을 Pd 증착 전과 후에 삽입하였으며, monchromatic XPS(x-ray photoelectron spectroscopy) 와 SAM(scanning Auger microscopy)을 사용하여 열처리 전과 40$0^{\circ}C$, 52$0^{\circ}C$ 그리고 695$0^{\circ}C$에서 3분간 열처리 후의 온도에 따른 morphology 변화, 계면반응(interfacial reaction) 및 벤드 휨(band bending)을 비교 연구하였다. Nls core level peak를 사용한 band bending에서 Schottky barrier height는 Pd/Ni bi-layer 접합시 2.1eV를, Ni/Pd bi-layer의 경우에 2.01eV를 얻었으며, 이는 Pd와 Ni의 이상적인 Schottky barrier height 값 2.38eV, 2.35eV와 비교해 볼 때 매우 유사한 값임을 알 수 있다. 시료를 후열처리함에 의해 52$0^{\circ}C$까지는 barrier height는 큰 변화가 없으나, $650^{\circ}C$에서 3분 열처리 후에 0.36eV, 0.28eV 만큼 band가 더 ？을 알 수 있었다. Pd/Ni 및 Ni/Pd 접합시 $650^{\circ}C$까지 후 열 처리 과정에서 계면에서 matallic Ga은 온도에 비례하여 많은 양이 형성되어 표면으로 편석(segregation)되어지나, In-situ SAM을 이용한 depth profile을 통해서 Ni/Pd, Pd/Ni는 증착시 uniform하게 성장함을 알 수 있었으며, 후열처리 함에 의해서 점차적으로 morphology 의 변화가 일어나기 시작함을 볼 수 있었다. 이는 $650^{\circ}C$에서 열처리 한후의 ex-situ AFM을 통해서 재확인 할 수 있었다. 이상의 결과로부터 GaN에 Pd를 접합 시 심한 clustering이 형성되어 Ohoic contact에 문제가 있으나 Pd/Ni 혹은 Ni/Pd bi-layer를 사용함에 의해서 clustering의 크기를 줄일 수 있었다. Clustering의 크기는 Ni/Pd bi-layer의 경우가 작았으며, $650^{\circ}C$ 열처리 후에 barrier height는 Pd/Ni bi-layer의 경우에도 Ni의 영향을 받음을 알 수 있었다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.164-167
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• 2002

The general dicing process cuts a semiconductor wafer to lengthwise and crosswise direction by using a rotating circular diamond blade. But inferior goods are made under the influence of several parameters in dicing process such as blade, wafer, cutting water and cutting conditions. Moreover we can not applicable this dicing method to GaN wafer, because the GaN wafer is harder than the other wafer such as SiO$_2$, GaAs, CaAsP, and AlCaAs. In order to overcome this problem, development of a new dicing process and determination of dicing parameters are necessary. This paper describes determination of several parameters - scribing depth, scribing force, scriber inclined angle, scribing speed, and factor for scriber replacement - for a new dicing machine using scriber.

• Journal of Electrical Engineering and information Science
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• v.2 no.4
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• pp.99-105
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• 1997

The new classified model for N-p heterojunction diode is derived and used extensively in analyzing the current-voltage(I-V) characteristics of the HBTs. A new classification method is presented in order to simplify I-V equations and easily applied to the modeling of HBTs. This classification method is characterized by the properties of devices such as high level injection, the thickness of one or both bulk regions, the surface recombination and the generation-recombination. The simulation results using the proposed model agree well with the experimentally observed I-V behaviors and show good efficiencies in its application to HBTs with respect to mathematical formulation.

• Electrical & Electronic Materials
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• v.12 no.8
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• pp.39-45
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• 1999

Comparative photoresponsive current-volt-age characteristics of n-channel PHEMT and MESFET on GaAs substrate. with (W/L)=200${\mu}{\textrm}{m}$/1${\mu}{\textrm}{m}$ of gates, are reported as a function of electro-optical stimulation (P\ulcorner, λ=830nm) for the first time as far as we know. Significantly different photoresponses are observed in MESFET and PHEMT, mainly due to different optoelectronic mechanisms in the formation and current conduction of channel carriers. Under high optical power, high photoresponsity with a strong non-linearity with P\ulcorner, predominantly due to a parallel conduction via a heavily doped Al\ulcornerGa\ulcornerAs donor layer, was observed in PHEMT while the optically induced drain current has been very small but monotonically increasing with optical stimulation in GaAs MESFET. We also investigated differences in optically stimulated gate leakage currents and photonic gate responses on gate voltage and drain voltage as a function of P\ulcorner. Based on the drain and gate responses to electro-optical stimulation. PHEMTs are expected to be a better candidate for high performance photonically responsive microwave device compared with MESFETs.

• JSTS:Journal of Semiconductor Technology and Science
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• v.4 no.1
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• pp.63-73
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• 2004

A simple analytical model has been presented for the study of the optical bistability using a $GaAs-Al_{0.32}Ga_{0.68}As$ multiple quantum well (MQW) p-i-n diode structure. The calculation of the optical absorption is based on a semi-emperical model which is accurately valid for a range of wells between 5 and 20 nm and the electric field F< 200kV/cm . The electric field dependent analytical expression for the responsivity is presented. An attempt has been made to derive the analytical relationship between the incident optical power ( $(P_{in})$ ) and the voltage V across the device when the diode is reverse biased by a power supply in series with a load resistor. The relationship between $P_{in}$ and $P_{out}$ (i.e. transmitted optical power) is also presented. Numerical results are presented for a typical case of well size $L_Z=10.5nm,\;barrier\;size\;L_B=9.5nm$ optical wave length l = 851.7nm and electric field F? 100kV/cm. It has been shown that for the values of $P_{in}$ within certain range, the device changes its state in such a way that corresponding to every value of $P_{in}$ , two stable states and one unstable state of V as well as of $P_{out}$ are obtained which shows the optically controlled bistable nature of the device.