Han-Young Lee

Interfacial reaction of atomic-layer-deposited HfO2 film as a function of the surface state of an n-GaAs (100) substrate

The characteristics of interfacial reactions and the valence band offset of HfO2 films grown on GaAs by atomic layer deposition were investigated by combining high-resolution x-ray photoelectron spectroscopy and high-resolution electron transmission microscopy. The interfacial characteristics are significantly dependent on the surface state of the GaAs substrate. Polycrystalline HfO2 film on a clean GaAs surface was changed to a well-ordered crystalline film as the annealing temperature increased, and a clean interface with no interfacial layer formed at temperatures above 600°C. The valence band offset of the film grown on the oxidized GaAs surface gradually increased with the stoichiometric change in the interfacial layer.

Efficient high-power frequency doubling of distributed Bragg reflector tapered laser radiation in a periodically poled MgO-doped lithium niobate planar waveguide

We report on efficient single-pass, high-power second-harmonic generation in a periodically poled MgO-doped LiNbO3 planar waveguide using a distributed Bragg reflector tapered diode laser as a pump source. A coupling efficiency into the planar waveguide of 73% was realized, and 1.07 W of visible laser light at 532 nm was generated. Corresponding optical and electro-optical conversion efficiencies of 26% and 8.4%, respectively, were achieved. Good agreement between the experimental data and the theoretical predictions was observed.

Changes in the structure of an atomic-layer-deposited HfO2 film on a GaAs (100) substrate as a function of postannealing temperature

The effects of postannealing temperature on the crystal structure and energy band gap (Eg) values of atomic-layer-deposited HfO2 films grown on a GaAs (100) substrate were investigated. In postannealed HfO2 films prepared using a rapid thermal annealing (RTA) process in a N2 ambient at temperatures over 600 °C, the initially produced, partially crystallized HfO2 film changed into a well-ordered crystalline structure with no detectable interfacial layer between the film and the GaAs substrate. In the case of a RTA prepared at 700 °C, the thickness of the film was relatively increased compared to that of an as-grown film. Changes in the depth profile data related to stoichiometry and electronic structure after the annealing treatment indicated that Ga oxide is formed within the HfO2 film during the RTA. The formation of Ga oxide in the film significantly affected the Eg values, i.e., the Eg changed from 5.5 for an as-grown film to 4.7 eV for a film annealed at 700 °C.

Effects of parasitic modes in high-speed LiNbO 3 optical modulators

The characteristics of RF parasitic modes and the methods to suppress leakage phenomena in LiNbO(3) optical modulators were studied. The high frequency RF power transmission characteristics were simulated and experimented in the respects of LiNbO(3) wafer thickness, the kind of material contacting the back surface of the modulator chip, the gap and width of the CPW (co-planar waveguide) electrodes. An appropriate RF electrode geometry, to minimize coupling efficiency between co-planar waveguide and substrate mode, is proposed. Experimental results prove that the approaches made in this work are effective for broadening of modulation bandwidth.

Characterization of channel strain evolution upon the silicidation of recessed source/drain Si1−xGex structures

This letter reports on Ni germanosilicide formation on recessed Si0.82Ge0.18 source/drain structures and its effects on channel strain. A combination of transmission electron microscopy techniques, including nanobeam diffraction, shed some light on a previously unrecognized factor in the channel strain evolution during silicidation: a Ge accumulation layer produced at the bottom of the germanosilicide layer. The formation of such a Ge rich layer added an additional compressive strain to the channel strain upon moderate silicidation, while the contribution of thermal strain arising from the cooling cycle became dominant in an excessively silicided sample, which turned the channel strain into a tensile value.

Wavelength selective single and dual-channel dropping in a periodically poled Ti:LiNbO 3 waveguide

All-optical wavelength selective single and dual channel dropping by sum frequency generation has been demonstrated in a periodically poled Ti:LiNbO(3) waveguide, which has two second harmonic phase-matching peaks. Less than -17 dB of channel dropping extinction ratio was observed with coupled pump power of 325 mW.

Achievement of a high channel strain via dry oxidation of recessed source/drain Si1−xGex structures

This study proposes a method of acquiring a high channel strain by locally oxidizing recessed Si1−xGex source/drain structures and forming a Ge condensation layer as an effective stressor. Combination of several transmission electron microscopy characterization techniques including nanobeam diffraction allowed us to analyze the thickness and composition of the Ge condensation layer formed upon oxidation, and the evolution of the channel strain. Nanobeam diffraction results demonstrate that this method can be critically used to effectively increase the channel strain.This study proposes a method of acquiring a high channel strain by locally oxidizing recessed Si1−xGex source/drain structures and forming a Ge condensation layer as an effective stressor. Combination of several transmission electron microscopy characterization techniques including nanobeam diffraction allowed us to analyze the thickness and composition of the Ge condensation layer formed upon oxidation, and the evolution of the channel strain. Nanobeam diffraction results demonstrate that this method can be critically used to effectively increase the channel strain.

Integrated optical modulator for signal up-conversion over radio-on-fiber link.

An integrated optical modulator, which consists of a dual-sideband suppressed carrier (DSB-SC) modulator cascaded with a single-sideband (SSB) modulator, is proposed for signal up-conversion over Radio-on-Fiber. Utilizing a single-drive domain inverted structure in both modulators, balanced modulations were obtained without complicated radio frequency (RF) driving circuits and delicate RF phase adjustments. Intermediate frequency (IF) band signal was up-conversed to 60GHz band by using the fabricated device and was transmitted over optical fiber. Experiment results show that the proposed device enables millimeter wave generation and signal transmission without any power penalty caused by chromatic dispersion.

Birefringent waveguide sensor using a polarizer rotating technique

A birefringence measurement system is introduced to get high phase resolution for detection of low contents of biochemicals. By using a fixed quarter-wave plate and a rotating polarizer, the phase difference between two orthogonal polarizations is transformed into phase delay of output sinusoidal signal. Analyzing the output phase, birefringence change could be detected with a phase noise of 0.14 degrees. As well as the birefringence measurement system, an optical evanescent waveguide sensor was developed. A rib-type silica waveguide overlaid with TiO2 film was fabricated, and a developed birefringence measurement technique was employed in evaluating a refractive index change on waveguide surface. For the fabricated waveguide with a 40-nm-thick TiO2 film, experiment results showed that the minimum detectable index change was 5.9x10(-7).

Spatial mode behavior of second harmonic generation in a ridge-type waveguide with a periodically poled MgO-doped lithium niobate crystal

We report on spatial mode behavior of the second harmonic (SH) generated by nonlinear interaction in the a z-cut Mg-doped periodically poled LiNbO3 (MgO:PPLN) ridge-type waveguide. Specific SH modes were selectively generated by mode mixing of the fundamental harmonic (FH) waves. In addition, high-order SH modes TM10 and TM01 were simultaneously generated under similar phase-matching conditions in a quasi-phase matching (QPM) grating structure. The interfered mode profiles of high-order SH modes demonstrated specific mode distribution to have a diagonal angle and the Laguerre–Gaussian (LG) mode at a certain phase-matching condition obtained by temperature control.