• 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 Electrical Engineering and Technology
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• v.9 no.5
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• pp.1654-1659
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• 2014

Tunneling field-effect transistors (TFETs) are very applicable to low standby-power application by their virtues of low off-current ($I_{off}$) and small subthreshold swing (S). However, low on-current ($I_{on}$) of silicon-based TFETs has been pointed out as a drawback. To improve $I_{on}$ of TFET, a gate-all-around (GAA) TFET based on III-V compound semiconductor with InAs/InGaAs/InP multiple-heterojunction structure is proposed and investigated. Its performances have been evaluated with the gallium (Ga) composition (x) for $In_{1-x}Ga_xAs$ in the channel region. According to the simulation results for $I_{on}$, $I_{off}$, S, and on/off current ratio ($I_{on}/I_{off}$), the device adopting $In_{0.53}Ga_{0.47}As$ channel showed the optimum direct-current (DC) performance, as a result of controlling the Ga fraction. By introducing an n-type InGaAs thin layer near the source end, improved DC characteristics and radio-frequency (RF) performances were obtained due to boosted band-to-band (BTB) tunneling efficiency.

• Korean Journal of Materials Research
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• v.3 no.5
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• pp.443-450
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• 1993

Self-alignment gatc Schottky contact structure on Si- implanted GaAs was formed by plasma enhanced chemical vapor dcposirion. Tungsten nitride thin films (ahclut 1600$\AA$) \vcre dopositcd on GaAs at $350^{\circ}C$ in order to fahricarc GaAs 1Cs and ttwn rapidly annealed at $750^{\circ}C$ to $900^{\circ}C$. Thermal charac tcristics of PECVD)-$W_{67}N_{43}$/GaAs structure were investigated by X-ray diffraction, photolumintesccnce. and optical deep level transient specrroscopy. Results revealed that $W_{67}N_{33}$ gate was more thermally sta ble with GaAs substrate than W gate and Si atoms implanted In $W_{67}N_{33}$/GaAs structure became morr active than those In W/GaAs after annealing. I-V characteristics of $W_{67}N_{33}$/GaAs diod c exhibired a nearly ideal diode behavior. The termal stability of $W_{67}N_{33}$/GaAs diode was better than that of W/GaAs diode with the post annealing at temperatures from 800 to $900^{\circ}C$ for 20s without As overpressure.

• Journal of Magnetics
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• v.13 no.3
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• pp.110-113
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• 2008

In this study, heavy rare earth garnet $Tb_2Bi_1Ga_1Fe_4O_{12}$ powders were fabricated by a sol-gel and vacuum annealing process. The crystal structure was found to be single-phase garnet with a space group of Ia3d. The lattice constant $a_0$ was determined to be 12.465 ${\AA}$. From the analysis of the vibrating sample magnetometer (VSM) hysteresis loop at room temperature, the saturation magnetization and coercivity of the sample are 7.64 emu/g and 229 Oe, respectively. The N$\acute{e}$el temperature($T_N$) was determined to be 525 K. The M$\ddot{o}$ssbauer spectrum of $Tb_2Bi_1Ga_1Fe_4O_{12}$ at room temperature consists of 2 sets of 6 Lorentzians, which is the pattern of single-phase garnet. From the results of the M$\ddot{o}$ssbauer spectrum at room temperature, the absorption area ratios of Fe ions on 24d and 16a sites are 74.7% and 25.3%(approximately 3:1), respectively. These results show that all of the non-magnetic Ga atoms occupy the 16a site by a vacuum annealing process. Absorption area ratios of Fe ions are dependent not only on a sintering condition but also on the temperature of the sample. It can then be interpreted that the Ga ion distribution is dependent on the temperature of the sample. The M$\ddot{o}$ssbauer measurement was carried out in order to investigate the atomic migration in $Tb_2Bi_1Ga_1Fe_4O_{12}$.

• Transactions on Electrical and Electronic Materials
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• v.14 no.1
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• pp.32-35
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• 2013

In this paper, a manufacturing process was developed for fabricating high-quality AlGaN/GaN high electron mobility transistors (HEMTs) on silicon carbide (SiC) substrates. Various conditions and processing methods regarding the ohmic contact and pre-metal-deposition $BCl_3$ etching processes were evaluated in terms of the device performance. In order to obtain a good ohmic contact performance, we tested a Ti/Al/Ta/Au ohmic contact metallization scheme under different rapid thermal annealing (RTA) temperature and time. A $BCl_3$-based reactive-ion etching (RIE) method was performed before the ohmic metallization, since this approach was shown to produce a better ohmic contact compared to the as-fabricated HEMTs. A HEMT with a 0.5 ${\mu}m$ gate length was fabricated using this novel manufacturing process, which exhibits a maximum drain current density of 720 mA/mm and a peak transconductance of 235 mS/mm. The X-band output power density was 6.4 W/mm with a 53% power added efficiency (PAE).

• Bulletin of the Korean Chemical Society
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• v.33 no.8
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• pp.2523-2528
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• 2012

Green phosphors $(Zn_{1-a-b}M_aM^{\prime}_b)_xGa_yS_{x+3y/2}:Eu^{2+}$ (M, M' = alkali earth ions) with x = 2 and y = 2-5 were prepared, starting from ZnO, MgO, $SrCO_3$, $Ga_2O_3$, $Eu_2O_3$, and S with a flux $NH_4F$ using a conventional solidstate reaction. A phosphor with the composition of $(Zn_{0.6}Sr_{0.3}Mg_{0.1})_2Ga_2S_5:Eu^{2+}$ produced the strongest luminescence at a 460-nm excitation. The observed XRD patterns indicated that the optimized phosphor consisted of two components: zinc thiogallate and zinc sulfide. The characteristic green luminescence of the $ZnS:Eu^{2+}$ component on excitation at 460 nm was attributed to the donor-acceptor ($D_{ZnGa_2S_4}-A_{ZnS}$) recombination in the hybrid boundary. The optimized green phosphor converted 17.9% of the absorbed blue light into luminescence. For the fabrication of light-emitting diode (LED), the optimized phosphor was coated with MgO using magnesium nitrate to overcome their weakness against moisture. The MgO-coated green phosphor was fabricated with a blue GaN LED, and the chromaticity index of the phosphor-cast LED (pc-LED) was investigated as a function of the wt % of the optimized phosphor. White LEDs were fabricated by pasting the optimized green (G) and the red (R) phosphors, and the commercial yellow (Y) phosphor on the blue chips. The three-band pc-WLED resulted in improved color rendering index (CRI) and corrected color temperature (CCT), compared with those of the two-band pc-WLED.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1996.11a
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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.

• Transactions on Electrical and Electronic Materials
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• v.7 no.1
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• pp.36-41
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• 2006

In this paper, the time evolution of undoped GaN epilayers on a low-temperature GaN buffer layer grown on c-plane sapphire at a low pressure of 300 Torr was studied via a two-step growth condition in a horizontal MOCVD reactor. As a function of the growth time at a high-temperature, the surface morphology, structural quality, and optical and electrical properties were investigated using atomic force microscopy, high-resolution x-ray diffraction, photoluminescence, and Hall effect measurement, respectively. The root-mean-square roughness showed a drastic decrease after a certain period of surface roughening probably due to the initial island growth. The surface morphology also showed the island coalescence and the subsequent suppression of three-dimensional island nucleation. The structural quality of the GaN epilayer was improved with increasing growth time considering the symmetrical (002) and asymmetrical (102) rocking curves. The variations of room-temperature photoluminescence, background carrier concentration, and Hall mobility were measured and discussed.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.7
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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.

• 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.