Jong-In Song

InAs nanowires on Si substrates grown by solid source molecular beam epitaxy

Au-activated InAs nanowires were grown on Si substrates by solid source molecular beam epitaxy (SSMBE). Epitaxial growth of InAs nanowires turned out to be very sensitive to the surface condition of the Si substrates. InAs nanowires having a growth direction, a high crystalline quality and a high aspect ratio over 300 with a uniform lateral size along the growth direction were grown using a high-temperature pre-annealing process in the MBE growth chamber to remove residual oxides from the surface of the Si substrates.

Growth of GaAs Nanowires on Si Substrates Using a Molecular Beam Epitaxy

Au-catalyzed GaAs nanowires were grown on Si substrates by vapor-liquid-solid growth method using a molecular beam epitaxy (MBE). The MBE growth could produce controlled crystalline orientation and uniform diameter along the wire axis of the GaAs nanowires by adjusting growth conditions including growth temperature and V/III flux ratio. Growths of GaAslang001rang as well as GaAslang111rang nanowires were observed by transmission electron microscopy and scanning electron microscopy. Epitaxially grown GaAslang111rang nanowires on a Si(111) substrate were verified through x-ray diffraction out-of-plane 2thetas/omega-scans. A strong room-temperature photoluminescence (PL) was observed from the epitaxially grown GaAslang111rang nanowires on a Si(100) substrate. Results of low-temperature (10 K) PL measurements and current-sensing atomic force microscopy indicated that the GaAs nanowires on a Si substrate were unintentionally doped with Si

GaAs nanowires on Si substrates grown by a solid source molecular beam epitaxy

High-quality Au-catalyzed GaAs nanowires were grown on Si substrates by vapor-liquid-solid growth in a solid source molecular beam epitaxy system. X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy reveal that the GaAs nanowires were epitaxially grown on Si substrates with uniform diameters along the nanowires. While GaAs nanowires on Si(111) and (001) substrates were mainly grown along the ⟨111⟩ direction with zinc-blende and wurtzite structures, unusual GaAs nanowires grown along ⟨001⟩ with a pure zinc-blende structure were also observed. Strong photoluminescence was observed from GaAs nanowires grown on a Si(001) substrate at room temperature.

Simultaneous WDM RoF Signal Generation Utilizing an All-Optical Frequency Upconverter Based on FWM in an SOA

A simultaneous all-optical frequency upconversion technique using four-wave mixing in a semiconductor optical amplifier (SOA) is experimentally demonstrated for wavelength-division-multiplexing (WDM) radio-over-fiber applications. Eight WDM optical radio-frequency (RF) signals having the RF frequency of 26.5 GHz are simultaneously generated by mixing eight WDM optical intermediate-frequency (IF) signals having the IF frequency of 2.5 GHz with an optical local oscillator signal of 24 GHz in a single SOA. The power penalty for simultaneous generation of eight WDM optical RF signals at the bit-error rate of 10-9 is less than 2.7 dB.

All-optical frequency downconversion technique utilizing a four-wave mixing effect in a single semiconductor optical amplifier for wavelength division multiplexing radio-over-fiber applications.

An all-optical frequency downconversion utilizing a four-wave mixing effect in a single semiconductor optical amplifier (SOA) was experimentally demonstrated for wavelength division multiplexing (WDM) radio-over-fiber (RoF) applications. Two WDM optical radio frequency (RF) signals having 155 Mbps differential phase shift keying (DPSK) data at 28.5 GHz were simultaneously down-converted to two WDM optical intermediate frequency (IF) signals having an IF frequency of 4.5 GHz by mixing with an optical local oscillator (LO) signal having a LO frequency of 24 GHz in the SOA. The bit-error-rate (BER) performance of the RoF up-links with different optical fiber lengths employing all-optical frequency downconversion was investigated. The receiver sensitivity of the RoF up-link with a 6 km single mode fiber and an optical IF signal in an optical double-sideband format was approximately -8.5 dBm and the power penalty for simultaneous frequency downconversion was approximately 0.63 dB. The BER performance showed a strong dependence on the fiber length due to the fiber dispersion. The receiver sensitivity of the RoF up-link with the optical IF signal in the optical single-sideband format was reduced to approximately -17.4 dBm and showed negligible dependence on the fiber length.

Generation and Transmission of a Quasi-Optical Single Sideband Signal for Radio-Over-Fiber Systems

Generation of a quasi-optical single sideband (OSSB) signal for a radio-over-fiber system utilizing the coherent population oscillation effects in a nonlinear semiconductor optical amplifier and transmission over a single-mode fiber (SMF) are investigated. The quasi-OSSB signal generator consists of an electroabsorption modulator and a nonlinear semiconductor optical amplifier. Characteristics of generated quasi-OSSB signals having different radio-frequency (RF) waves (1-50 GHz) transmitted over SMFs of different lengths (4-21 km) were investigated. Bit-error-rate performance of quasi-OSSB signals having 155-Mb/s differential phase-shift keying (DPSK) data transmitted over 0- to 55-km-long SMFs was also evaluated.

A Capless

Characteristics of a 0.2-mum capless InAlAs/InGaAs pseudomorphic high electron mobility transistor (p-HEMT) having a self-aligned gate (SAG) were investigated. The 0.2-mum SAG capless p-HEMT showed a source resistance comparable to that of a conventional recessed p-HEMT having a heavily n-doped In_0.53Ga_0.47As cap layer primarily due to the SAG and optimized ohmic-metallization processes and excellent characteristics of G_m,max, f_T, and f_max of 1.12 S/mm, 185 GHz, and 225 GHz, respectively, even without a heavily doped InGaAs cap layer. The capless device exhibited much better device parameters for digital logic applications including I _ON/I_OFF and subthreshold slope (1.27times10⁴ and 78 mV/dec) compared with those (5.1times10³ and 120 mV/dec) of the conventional recessed device, respectively

hboxInP/hboxIn_0.52hboxAl_0.48hboxAs/hboxIn_0.53hboxGa_0.47hboxAs

We investigated the effects of high temperature (∼700°C) in situ rapid thermal annealing (RTA) carried out during growth interruption between spacer and δ-doping layers of an In0.52Al0.48As∕In0.53Ga0.47As metamorphic high electron mobility transistor (MHEMT) grown on a compositionally graded InGaAlAs buffer layer. The in situ RTA improved optical and structural properties of the MHEMT without degradation of transport property, while postgrowth RTA improved the structural property of the MHEMT but significantly degraded mobility due to the defect-assisted Si diffusion. The results indicate the potential of the in situ RTA for use in the growth of high-quality metamorphic epitaxial layers for optoelectronic applications requiring improved optical and electrical properties.

p-HEMT Having a Self-Aligned Gate Structure

A transient electrooptic near-field mapping system based on a gain-switched distributed feedback (DFB) pulsed laser and a CdTe electrooptic crystal was used for characterizing transient near-field patterns of conventional and uniplanar compact photonic bandgap (UC-PBG) patch antennas fabricated on a low-cost FR4 substrate. Effect of the UC-PBG structure on reduction in surface waves in the UC-PBG patch antenna was investigated experimentally by comparing transient near-field patterns of the conventional and UC-PBG patch antennas

Molecular beam epitaxy growth of In0.52Al0.48As∕In0.53Ga0.47As metamorphic high electron mobility transistor employing growth interruption and in situ rapid thermal annealing

Structural and carrier dynamic properties of low-temperature-grown In0.53Ga0.47As (LT-InGaAs) on GaAs using an InGaAlAs metamorphic buffer were studied. Investigation of dependence of the structural and carrier dynamic properties of the LT-InGaAs on annealing temperature showed that they were closely related. The use of the metamorphic buffer was effective in reducing the carrier lifetime in the LT-InGaAs. A carrier lifetime as short as 2.14ps, comparable to that of Be-doped LT-InGaAs was achieved.