Ki-Won Seo

For the fast droplet transportation on an open surface, a new magnetic elastomer with a superhydrophobic surface has been developed. Because the surface is superhydrophobic, the water droplet can easily roll off on the surface. The movement of the droplet was controlled by a deliberate local deformation of the surface of the elastomer induced by magnetic actuation. The direction and speed of the droplet motion was easily controlled by changing the surface topography using magnetic force. We also

The high optical responsivity of the InAlAs-InGaAs metamorphic high-electron mobility transistor on GaAs substrate with composite channels is reported. Experimental results verify that the photovoltaic effect causing the effective decrease of threshold voltage is responsible for the photoresponse to a 1.55-μm optical illumination.

We have used reflection high-energy electron diffraction (RHEED) to study the surface recovery of AlGaAs under different conditions. A modified process for growth interruptions was then introduced, where a GaAs monolayer was grown at each growth stop, and the arsenic flux was turned off during the low-temperature phase of growth interruptions. Selectively doped inverted heterojunctions were grown using the modified growth interruptions together with low-growth temperature (to avoid Si and impuri

A new ultra-wideband, low-loss and small-size coplanar waveguide (CPW) to coplanar strip (CPS) transition which can be used from DC to 110 GHz is presented. The proposed transition connects CPW with CPS by the reformed air-bridge. Two ground planes of CPW are tied at their ends by a line and the centre of the line is connected to the ground strip of CPS by another line. Owing to the symmetry of the proposed structure, the currents of two ground planes of CPW are combined with the same phase and

A high-gain ballistic hot-electron device is described. The GaAs-AlGaAs heterostructure device, with a 21-mm-thick pseudomorphic In/sub 0.12/Ga/sub 0.88/As base, had a current gain of 27 at 77 K and 41 at 4.2 K. As characteristically seen in ballistic devices, transfer into the L valley limited the maximum gain. The Gamma -L valley separation in the strained In/sub 0.12/Ga/sub 0.88/As was estimated to be about 380 meV.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.

In0.53Ga0.47As/ In0.52Al0.48As single quantum well structures grown by molecular beam epitaxy were pulse annealed by a halogen lamp to determine the stability of their optical properties after such thermal treatment. The annealing time and temperature were 5 s and 650–850 °C, respectively. The shift in energy of the main peak in the low-temperature photoluminescence spectra was modeled by considering Al-Ga interdiffusion at the heterointerface and solving the appropriate Schrödinger equation for

We report the first direct observation of ballistic hole transport in semiconductors, via energy spectroscopy experiments. Light holes are preselected and injected via tunneling into 31-nm-thick ${\mathrm{p}}^{+}$ GaAs layers. About 10% of the injected holes have been found to travel ballistically maintaining distributions \ensuremath{\simeq}35 meV wide, with a mean free path of about 14 nm. Resonances in the injection currents, resulting from quantum interference effects of the ballistic holes,

High-mobility III-V transistors are poised to take the lead on future high performance logic operation. If this happens, indium-rich In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> As is the most promising n-channel material. Indeed, remarkable progress has been made, including III-V gate-stacks with ALD-grown gate dielectrics. This

We have successfully grown δ-doped AlGaAs structures and δ-doped AlGaAs/InGaAs pseudomorphic high electron mobility transistor (HEMT) structures by atmospheric pressure metalorganic chemical vapor deposition (MOCVD). Capacitance-voltage (C-V) profiles with full-width at half-maximum as small as 32 Å demonstrate very narrow doping profiles of δ-doped AlGaAs layers grown at 650–700 °C. Theoretical C-V profiles of δ-doped AlGaAs have been self-consistently calculated with the L valley taken into ac

A W-band divide-by-3 frequency divider with wide bandwidth and low power dissipation is presented using harmonic injection-locking technique. A cascode FET is employed for a self-oscillating second-harmonic mixer which is injection-locked by third-harmonic input to obtain the division order of three. The fabricated frequency divider using 0.1 µm GaAs metamorphic HEMT technology shows superior performance such as large bandwidth of 6.1 GHz around 83.1 GHz (7.3%) under small DC power consumption o

We report the first successful incorporation of a pseudomorphic InGaAs base in a ballistic hot-electron device. The device, with a 28-nm-thick In0.15Ga0.85As base, had a collector-base breakdown voltage of 0.55 V and a maximum current transfer ratio of 0.89 at 4.2 K, considerably higher than the 0.75 in a comparable GaAs-base device. Electron energy spectroscopy measurements revealed that at least 30% of the injected electrons traversed the InGaAs base ballistically, causing a strong modulation

The successful application of short-term halogen lamp annealing to form ohmic contacts to AlGaAs/GaAs and In 0.52 Al 0.48 As/ In 0.53 Ga 0.47 As modulation-doped structures is demonstrated. Use of Ti in the electron-beam evaporated metallization scheme and a two-step annealing cycle give contacts with reproducibly good electrical and morphological characteristics. Minimum values of specific contact resistance \rho_{c} = 4.0 \times 10^{-7} and 6.0 \times 10^{-7} Ω.cm2for AlGaAs/GaAs and In 0.52 A

The DC and microwave performance of a modulation-doped InGaAs/InAlAs quasi-MISFET structure, grown by molecular beam epitaxy, is reported. Improved performance is obtained with the incorporation of Ti in the source-drain metallisation with which contact resistances as low as 0.1 Ωmm are measured. An extrinsic transconductance of 310mS/mm and a best value of fT=32 GHz in a 1.0 μ-gate device are measured at 300 K.

Thermal reliability of nickel (Ni) and copper (Cu) gate AlGaN/GaN high electron mobility transistors (HEMTs) is investigated. Though the current-voltage characteristics of as-deposited Cu gate AlGaN/GaN HEMTs is superior to those of Ni gate AlGaN/GaN HEMTs, severe degradation was observed after aging at 220°C. This instability problem should be carefully taken into account in practical applications of Cu gate AlGaN/GaN HEMTs.

A simple balun having the structure of a Wilkinson divider is proposed, and a 77 GHz CPW balun, as an example, has been fabricated and measured. The input and output ports of the proposed Wilkinson balun form the desirable inline structure. Results show that the measured S21, S31, matching, and isolation are −4.5 and −3.7 dB, less than −15 and −20 dB with the exact out of phase between output ports.