• Proceedings of the IEEK Conference
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• 1998.06a
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• pp.405-408
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• 1998

Due to the large conduction band discontinuity between emitter base, OmGaAs HBT has an advantge to enable the hot electrons to inject into the base. In this paper, InAlGaAs/InGaAs HBT with the various emitter junction gradings and the modified collectors are simulated and analyzed by HMC(hybrid monte carlo) simulator in order to find a optimal structure for the shortest transit time. A minium base transit time (.tau.$_{b}$ ) of 0.21 ps was obtained for HBT with the grading layer, which is parabolically graded from x=1.0 to x=0.5. The minimum collector transit time (.tau.$_{c}$ ) of 0.31ps was found when the collector was modified by inserting p$^{[-10]}$ and p$^{+}$ layers. Thus HBT in combination with the emitter grading and the modified collector layer showed the cut-off frequency (f$_{T}$) of 183GHz.z.z.

• Electrical & Electronic Materials
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• v.10 no.9
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• pp.922-929
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• 1997

As the size of semiconductor devices shrinks in the horizontal as well as vertical dimension it is difficult to estimate the transport-velocity of electron because they drift in non-equilibrium with a few scattering. In this paper HYbrid Monte Carlo simulator which employs the drift-diffusion model for hole-transport and Monte Carlo model for electron-transport in order to reduce the simulation time and increase the accuracy as well has been developed and applied to analyze the electron-transport in InAlAs/InGaAs HBT which is attractive for an ultra high speed active device in high speed optical fiber transmission systems in terms of the velocity and energy distribution as well as cutoff frequency.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.3
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• pp.66-74
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• 1999

InAlGaAs/InGaAs HBTs with the various emitter junction gradings(xf=0.0-1.0) and the modified collector structures (collector- I;n-p-n, collector-II;i-p-n) are simulated and analyzed by HMC (Hybrid Monte Carlo) method in order to find an optimum structure for the shortest transit time. A minimum base transit time($ au$b) of 0.21ps was obtainsed for HBT with the grading layer, which is parabolically graded from $x_f$=1.0 and xf=0.5 at the emitter-base interface. The minimum collector transit time($\tau$c) of 0.31ps was found when the collector was modified by inserting p-p-n layers, because p layer makes it possible to relax the electric field in the i-type collector layer, confining the electrons in the $\Gamma$-valley during transporting across the collector. Thus InAlGaAs/InGaAs HBT in combination with the emitter grading($x_f$=0.5) and the modified collector-III showed the transit times of 0.87 psec and the cut-off frequency (f$\tau$) of 183 GHz.

• Journal of the Korean Vacuum Society
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• v.12 no.4
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• pp.218-227
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• 2003

Pd/Si/Ti/Pt and Pd/Si/Pd/Ti/Au ohmic contacts to n-type InCaAs were investigated for applications to AlGaAs/GaAs HBT emitter ohmic contacts. In the Pd/Si/Ti/Pt ohmic contact, as-deposited contact showed non-ohmic behavior, and high specific contact resistivity of $5\times10^{-3}\Omega\textrm{cm}^2$ was achieved by rapid thermal annealing at $375^{\circ}C$/10 sec. However, the specific contact resistivity decreased remarkably to $2\times10^{-6}\Omega\textrm{cm}^2$ by annealing at $425^{\circ}C$/10sec. In the Pd/Si/Pd/Ti/Au ohmic contact, minimum specific contact resistivity of $3.9\times10^{-7}\Omega\textrm{cm}^2$ was achieved by annealing at $400^{\circ}C$/20sec. In both ohmic contacts, low contact resistivity and non-spiking planar interface between ohmic materials and InGaAs were maintained. Therefore, these thermally stable ohmic contact systems are promising candidates for compound semiconductor devices. RF performance of the AlGaAs/GaAs HBT was also examined by employing the Pd/Si/Ti/Pt and Pd/Si/Pd/Ti/Au systems as emitter ohmic contacts. Cutoff frequencies were 63.9 ㎓ and 74.4 ㎓, respectively, and maximum oscillation frequencies were 50.1 ㎓ and 52.5 ㎓, respectively. It shows very successful high frequency operations.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07a
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• pp.366-370
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• 2002

GaAs has become a very popular material for the fabrication of high frequency, low noise and microwave power devices. GaAs devices are also well suited for high temperature operation because of the large band gap of this material. The standard GaAs technology and device structures have to be modified for stable operation at high temperature. In this paper, AlGaAs/GaAs HBT considering stable ohmic contact at high temperature as well as thermal effect such as self-heating effect are introduced. All the data obtained study will be used as input data for the simulator and the result will be compared with an analytical model available in this study,

• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.7
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• pp.88-93
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• 1998

For the self-aligned AlGaAs/GaAs HBTs, the surface states at the interface between the extrinsic base surface and the passivation nitride is a major cause of degradation of dc characteristics. In this paper the degradation mechanisms of self-aligned AlGaAs/GaAs HBT were analyzed, and GaAs HBTs, which employed an InGaP ledge emitter structure formed by the nonself-aligned process to cover the surface of the extrinsic base and reduce the surface states, produced high reliability. Accoridng to the acceleration lifetime test, the nonself-aligned InGaP/GaAs HBTs produced very reliable dc characteristics comparing with the self-aligned AlGaAs/GaAs HBTs. The activation energy was 1.97eV and MTTF $4.8{\times}10^{8}$ hrs at $140^{\circ}C$ which satisfied the MIL standard.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.5
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• pp.40-47
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• 1998

This paper report sthe design, fabrication and characterization of an AlGaAs/GaAs HBT (heterojunction bipolar transistor) with an air-bridge isolation structure which is made to improve high frequency characteristics for the application to the mobile communication system in the next genration. We found that the size, shape and structure of HBT have an effect on the high frequency operation. The measured dc and ac characteristics of the four type HBTs were compared and analyzed. An E-type HBT with an air-bridge structure by undercut etching exhibited .beta.=56, $V_{off-set}$ = 0.3 V, B $V_{CEO}$=7.0V with $f_{T}$=40 GHz and $f_{max}$=45GHz at a collector current density of 7.1*10$^{4}$ A/c $m^{2}$.>.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.32A no.2
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• pp.57-65
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• 1995

The effects of device geometry and layout on high speed performance such as current gain outoff frequency(f$_{T}$) and maximum oscillation frequency(f$_{max}$) are of very improtant for the scaling-down of geterojunction bipolar transistors(HBT$_{s}$). In this paper AlGaAs/GaAs HBTs are fabricated by MBE epitaxial growth and conventional mesa process, and the experimental data of emitter-base geometru dependency of HBT performance are presented in order to provide the quantitative information for optimum device structure design. It is shown that f$_{T}$ and f$_{max}$ are inversely proportional to the emiter stripe width, while the low emitter perimeter/area ratio is better to f$_{T}$ and worse ot f$_{max}$. It is also demonstrated the f$_{T}$ and f$_{max}$ are highly improved by the emitter-base spacing reduction resulting in less parsitic effects. As the result f$_{T}$ of 42GHz and f$_{max}$ of 23GHz are obtained for fabricated HBT with emitter area of 3${\times}20^{\mu}m^{2}$ and E-B spacing of 0.2$\mu$m.m.m.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.840-843
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• 2001

In this study, temperature dependency of current gain for AlGaAs/GaAs/GaAs HBT is analytically proposed over the temperature range between 300K and 600K. Energy bandgap, effective mass, intrinsic carrier concentration are considered as temperature dependent parameters. Collector current which is numerically calculated is then analytically expressed to enhance the speed of calculation for current gain. From the results, current gain decreases as the temperature increases. These results will be used to expect the unity current gain frequency f$_{T}$ in conjunction with emitter-base and collector- base capacitances.s.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.3C
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• pp.234-240
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• 2002

A power amplifier with AlGaAs/InGaAs/GaAs HBT's has been developed for customer premise equipments of the quasi millimeter-wave frequency-band broadband wireless local loop(BWLL) system. Parameters of the linear and nonlinear equivalent circuits for a common base HBT have been extracted by a fitting method. The amplifier has been designed through the linear and nonlinear circuit simulations and fabricated on a ceramic substrate for a hybrid IC. The amplifier has produced a 25.5-dBm output power with 35% power-added efficiency(PAE) at 24.4 GHz and achieved a 7.5-dB linear power gain at 24.8 GHz. In 24.25 ∼24.75 GHz band, the amplifier has exhibited a saturated output over larger than 22 dBm and PAE higher than 25%.