• JSTS:Journal of Semiconductor Technology and Science
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• v.15 no.5
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• pp.490-496
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• 2015

We have grown AlN/GaN heterostructure which is a promising candidate for mm-wave applications. For the growth of the high quality very thin AlN barrier, indium was introduced as a surfactant at the growth temperature varied from 750 to $1070^{\circ}C$, which results in improving electrical properties of two-dimensional electron gas (2DEG). The heterostructure with barrier thickness of 7 nm grown at of $800^{\circ}C$ exhibited best Hall measurement results; such as sheet resistance of $215{\Omega}/{\Box}$electron mobility of $1430cm^2/V{\cdot}s$, and two-dimensional electron gas (2DEG) density of $2.04{\times}10^{13}/cm^2$. The high electron mobility transistor (HEMT) was fabricated on the grown heterostructure. The device with gate length of $0.2{\mu}m$ exhibited excellent DC and RF performances; such as maximum drain current of 937 mA/mm, maximum transconductance of 269 mS/mm, current gain cut-off frequency of 40 GHz, and maximum oscillation frequency of 80 GHz.

• Electrical & Electronic Materials
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• v.12 no.8
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• pp.10-17
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• 1999

본 논문에서는 최근 초고주파영역에서 우수한 고출력 특성을 갖는 것으로 알려진 AlGaN-GaN high-electron mobility transistor(HEMT's)의 최근 기술동향과 함께 응용가능성 및 한계에 대하여 검토하였다. GaN는 약 3.4eV 정도의 큰 밴드갭을 갖는 까닭에 200V 이상의 높은 항복전압을 갖는다. 또한 AlGaN와 이종접합을 형성하는 경우 piezoelectric field에 의하여 1$\times$10\ulcornercm\ulcorner 이상의 높은 밀도의 2DEG(two-dimensional electron gas)의 형성이 가능하고, 상온 전자이동도가 1,200$\textrm{cm}^2$/V-s 이상으로서 초고주파 고출력 전자소자의 구현에 필요한 물성을 갖추고 있다. 현재 cutoff frequency fT가 60GHz이상, maximum frequency fmax가 150GHz 이상의 소자가 개발되었으며, 3W/cm 이상의 cw(continuous wave) 전력밀도가 보고된바 있다. 또한 열전도도가 큰 새로운 기판이 개발되고, heat dissipation을 개선하기 위한 새로운 소자구조가 개발됨에 따라 보다 높은 전력밀도를 갖는 단위소자 또는 MMIC(monolithic microwave integrated circuits)의 구현가능성이 높아지고 있다.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.7
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• pp.56-61
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• 1997

I $n_{0.53}$G $a_{0.47}$As/I $n_{0.52}$A $l_{0.48}$As pseudomorphic high electron mobility transistor (P-HEMT) structures were grown on semi-insulating InP substrates by molecular beam epitzxy method. The hall effect measuremetn was used to measure the electrical properties and the photoluminescence (PL) measurement was used to measure the electrical properties and the photoluminescence(PL) measurement for optical propety. By the cross-sectional transmission electron microscopy (XTEM) investigation of the V and X shape defects including slip with angle of 60.deg. C and 120.deg. C to surface in the sampel, the defects formation mecahnism in the I $n_{0.52}$A $l_{0.48}$As epilayers on InP substrates could be explained with the different thermal expansion coefficients between I $n_{0.52}$A $l_{0.48}$As epilayers and InP substrate.d InP substrate.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.54 no.3
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• pp.109-113
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• 2005

It has been reported that the failure phenomenon and variation of electrical characteristic due to the effect of electrostatic discharge(ESD) in silicon devices. But we had fess reports about the phenomenon due to the ESD in the compound semiconductors. So there are a lot of difficulty to the phenomenon analysis and to select the protection method of main circuits or the devices. It has not been reported that the relation between the ESD stress and GaN devices, which is remarkable to apply the operation in high temperature and high voltage due to the superior material characteristic. We studied that the characteristic variation of the AlGaN/GaN HEMT current, the leakage current, the transconductance(gm) and the failure phenomenon of device due to the ESD stress. We have applied the ESD stress by transmission line pulse(TLP) method, which is widely used in ESD stress experiments, and observed the variation of the electrical characteristic before and after applying the ESD stress. The on-current trended to increase after applying the ESD stress. The leakage current and transconductance were changed slightly. The failure point of device was mainly located in middle and edge sides of the gate, was considered the increase of temperature due to a leakage current. The GaN devices have poor thermal characteristic due to usage of the sapphire substrate, so it have been shown to easily fail at low voltage compared to the conventional GaAs devices.

• JSTS:Journal of Semiconductor Technology and Science
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• v.3 no.1
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• pp.13-20
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• 2003

Both MgO and $Sc_2O_3$ are shown to provide low interface state densities (in the $10^{11}{\;}eV^{-1}{\;}cm{\;}^{-2}$ range)on n-and p-GaN, making them useful for gate dielectrics for metal-oxide semiconductor(MOS) devices and also as surface passivation layers to mitigate current collapse in GaN/AlGaN high electron mobility transistors(HEMTs).Clear evidence of inversion has been demonstrated in gate-controlled MOS p-GaN diodes using both types of oxide. Charge pumping measurements on diodes undergoing a high temperature implant activation anneal show a total surface state density of $~3{\;}{\times}{\;}10^{12}{\;}cm^{-2}$. On HEMT structures, both oxides provide effective passivation of surface states and these devices show improved output power. The MgO/GaN structures are also found to be quite radiation-resistant, making them attractive for satellite and terrestrial communication systems requiring a high tolerance to high energy(40MeV) protons.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.476-477
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• 2013

반도체의 성능은 최근 10년 사이에 급격하게 발전했고 아날로그 및 디지털 회로 소자들에 있어 저전력/고속 특성 요구가 커지고 있다 [1]. 상온에서 30,000 $cm^2$/Vs 이상의 전자 이동도를 가지며 큰 conduction band offset을 갖는 InAs/AlSb 2차원전자가스(2DEG) 소자는 Spinorbit-interaction의 값이 매우 커서 SPIN-FET 소자로 크게 주목받고 있다 [2]. 본 발표자들은 GaAs 기판위에 성장한 InAs 2DEG HEMT 소자의 전/자기적인 특성과 고속반응 물질로 주목 받는 InSb 박막소자의 doping 특성에 따른 전기적/물리적인 특성의 평가에 대해 그 결과를 소개하고자 한다. 격자정합과 Semi-insulating 기판의 부재로 상용화되어 있는 GaAs와 InP 기판위에 물질차이에 따른 고유의 한계 특성을 줄이기 위한 Pseudomorphic이라 불리는 특별한 박막 성장 기법을 적용하여 높은 전자 이동도를 가지며 spin length가 길어 Spin-FET로서 크게 주목받고 있는 InAs 2DEG HEMT 소자를 완성시켰다. 60,000 ($cm^2$/Vs) 이상의 높은 전자 이동도를 갖는 소자의 구현을 목표로 연구를 진행하였으며 1.8 K에서 측정된 Spin-orbit interaction의 값은 6.3e-12 (eVm)이다. InAs/InGaAs/InAlAs 및 InGaAs/InAlAs 구조의 InP 기반의 소자에서 보다 큰 값으로 향후 Spin-FET 응용에 크게 기대하고 있다. 또한, GaAs 기판위에 구현된 InSb 소자는 격자부정합 감소를 위해 InAs 양자점을 사용하여 약 $2.6{\mu}m$ 두께로 구현된 InSb 박막 소자는 상온에서 약 60,400 ($cm^2$/Vs)의 상온 전자이동도를 보였으며 현재 동일 두께에서 세계 최고결과(~50,000 $cm^2$/Vs)에 비해 월등하게 높은 값을 보이고 있다. Hall bar pattern 공정을 거쳐 완성된 소자는 측정 결과 10~20% 이상 향상된 전자 이동도를 보였다. 2e18/$cm^3$ 미만의 p-doping의 경우, 상온에서 n-type 특성을 보이나, 저온에서 p-type으로 변하는 특성을 보였고 n-doping의 경우 5e17/$cm^3$까지는 전자 이동도만 감소하고, doping에 의한 효과는 크게 없었다. 1e18/$cm^3$의 높은 doping을 할 경우 carrier가 증가하는 것을 확인했다. 이상의 측정 결과로 Spin-FET 소자로서 아주 우수하다는 것을 확인할 수 있었고 n-/p- type이 특성을 고려한 high quality InSb 박막소자의 응용을 위한 중요한 정보를 얻을 수 있었다.

• Journal of the Semiconductor & Display Technology
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• v.12 no.3
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• pp.23-27
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• 2013

This paper is for enhancing the breakdown voltage of MHEMTs with an InP-etchstop layer. Gate-recess structures has been simulated and analyzed for the breakdown of the devices with the InP-etchstop layer. The fully removed recess structure in the drain side of MHEMT shows that the breakdown voltage enhances from 2V to almost 4V and that the saturation current at gate voltage of 0V is reduced from 90mA to 60mA at drain voltage of 2V. This is because the electron-captured negatively fixed charges at the drain-side interface between the InAlAs barrier layer and the $Si_3N_4$ passivation layer deplete the InGaAs channel layer more and thus decreases the electron current passing the channel layer. In the paper, the fully-recessed asymmetric gate-recess structure at the drain side shows the on-breakdown voltage enhancement from 2V to 4V in the MHEMTs.

• JSTS:Journal of Semiconductor Technology and Science
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• v.4 no.2
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• pp.117-123
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• 2004

A 30 nm $In_{0.7}GaAs$ High Electron Mobility Transistor (HEMT) with triple-gate has been successfully fabricated using the $SiO_2/SiN_x$ sidewall process and BCB planarization. The sidewall gate process was used to obtain finer lines, and the width of the initial line could be lessened to half by this process. To fill the Schottky metal effectively to a narrow gate line after applying the developed sidewall process, the sputtered tungsten (W) metal was utilized instead of conventional e-beam evaporated metal. To reduce the parasitic capacitance through dielectric layers and the gate metal resistance ($R_g$), the etchedback BCB with a low dielectric constant was used as the supporting layer of a wide gate head, which also offered extremely low Rg of 1.7 Ohm for a total gate width ($W_g$) of 2x100m. The fabricated 30nm $In_{0.7}GaAs$ HEMTs showed $V_{th}$of -0.4V, $G_{m,max}$ of 1.7S/mm, and $f_T$ of 421GHz. These results indicate that InGaAs nano-HEMT with excellent device performance could be successfully fabricated through a reproducible and damage-free sidewall process without the aid of state-of-the-art lithography equipment. We also believe that the developed process will be directly applicable to the fabrication of deep sub-50nm InGaAs HEMTs if the initial line length can be reduced to below 50nm order.

• 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.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.44 no.4
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• pp.80-85
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• 2007

The passivation is one of the important technologies for protection of the devies from damage. In this paper, we fabricated $0.1{\mu}m\;{\Gamma}$--gate InAIAs/InGaAs metamorphic high electron mobility transistors (MHEMTs) on a GaAs substrate. And then the wafer with MHEMTs was divided into two pieces; one for passivation and another for without passivation experiments. The passivations were done by using both low-k BCB and Si3N4 thin films. DC and RF performances were measured and the results are compared. The MHEMTs with BCB passivation show lower degradation than ones with Si3N4 passivation.