Mau Phon Houng

A novel compact ring dual-mode filter with adjustable second-passband for dual-band applications

In this letter, a novel compact ring dual-mode with adjustable second-passband for dual-band applications are presented. A ring resonator with two different geometric dimensions are derived and designed to have identical fundamental and the first higher-order resonant frequencies, and to establish appropriate couplings in the structure. Moreover, the proposed filter has smaller size as compared with the basic topology of stopband filters and stepped-impedance-resonator (SIR) filters. The measured filter performance is in good agreement with the simulated response.

A novel cross-shape DGS applied to design ultra-wide stopband low-pass filters

This letter presents a novel low-pass filter with an ultra-wide stopband. The proposed filter is comprised of a new cross-shape defected ground structure (CSDGS). By using this structure, the filter not only supports conventional DGS performances with a sharp rejection, but also exhibits an ultra-wide stopband. For the deigned low-pass filter, an insertion loss of less than 2dB from dc to 3.5GHz and the rejection is better than 20dB from 4.3 to 15.8GHz. Predicted performances show widened and deepened stopband beyond the low passband. Furthermore, it is confirmed by measurement.

CURRENT TRANSPORT MECHANISM IN TRAPPED OXIDES : A GENERALIZED TRAP-ASSISTED TUNNELING MODEL

A generalized trap-assisted tunneling (GTAT) model is proposed in this work, where an effective tunneling barrier of trapezoidal shape is considered, instead of the triangular barrier utilized in the conventional trap-assisted tunneling (TAT) model. It is demonstrated that trapezoidal barrier tunneling dominates at low electric fields (E<4 MV/cm), while triangular barrier tunneling contributes the main part of the tunneling current at high electric fields (E=6–8 MV/cm). The comparisons of this improved model and the results of the conventional TAT model at high and low electric fields are discussed. It is concluded that GTAT can more accurately model the current density-electric field (J–E) curves for the conduction enhancement of a trapped oxide film under various deposition conditions over a wider range of electric fields. This is confirmed by the comparative use of both TAT and GTAT models on experimental data obtained from existing reports. Furthermore, a simple method for determining the trap energy ...

Liquid Phase Chemical-Enhanced Oxidation for GaAs Operated Near Room Temperature

A new chemical enhanced oxidation method for gallium arsenide (GaAs) in liquid phase near room temperature (40°C–70°C) is proposed and investigated. Featureless oxide layers with good uniformity and reliability can be grown efficiently on GaAs without any extra energy source. A relatively high oxidation rate (1000 A/h), about 50 times higher than that obtained during oxidation in boiling water has been realized. Based on the results of X-ray photoelectron spectroscopy (XPS), excellent chemical stability after thermal annealing as well as good chemical stoichiometry have been realized. The oxide was determined to be composed of Ga2O3 and As2O3.

Enhancement of the light output performance for GaN-based light-emitting diodes by bottom pillar structure

A three-dimensional model with finite difference and time domain was established to investigate the enhancement of the light output intensity of GaN light-emitting diodes (LEDs) with bottom pillar (BP) structure. Through comparing the normalized light extraction intensity of GaN LEDs with or without BP in different dimensions, the theoretical results show that the light output intensity in the LED with BP structure involved could be enhanced by about 30%. The influence of BP structure on the light output intensity of a LED could be explained by the physical model of light interaction. In addition, the experimental results also show the same trend to the theoretical calculations.

Investigation in Open Circuited Metal Lines Embedded in Defected Ground Structure and Its Applications to UWB Filters

A novel method for notch implementation in ultrawideband (UWB) bandpass filter (BPF) using open circuited metal lines embedded in a defected ground structure (DGS) is proposed. Distinct from traditional notch implementation, the proposed method uses the additional metal lines with half waveguide length embedded in defected ground structure to produce additional notch band behavior based on the DGS bandpass behavior. Furthermore, the equivalent circuit model of the proposed UWB BPF with notch implementation is established for explaining the circuit behaviors more explicitly. In this way, the proposed circuit has a very small size, only amounting to 0.41 by 0.22 guided wavelength at the center frequency of 6.85 GHz. The experimental filter has a notch band frequency of 5.5 GHz, with two observable attenuation poles at 1.65 and 11.36 GHz, respectively. The measured BPF insertion loss is less than 1.0 dB throughout the passband of 3.1 to 10.6 GHz, and the variation of group delay is less than 0.2 ns in this band, except for the notched band.

A GaAs MOSFET with a liquid phase oxidized gate

Low leakage current density (as low as 10/sup -8/ A/cm/sup 2/ at an applied voltage of 5 V) and high breakdown electrical field (larger than 4.5 MV/cm) of the liquid phase chemical-enhanced oxidized GaAs insulating layer enable application to the GaAs MOSFET. The oxide layer is found to be a composite of Ga/sub 2/O/sub 3/, As, and As/sub 2/O/sub 3/. The n-channel depletion mode GaAs MOSFETs are demonstrated and the I-V curves with complete pinch-off and saturation characteristics can be seen. A transconductance larger than 30 mS/mm can be achieved which is even better than that of MESFETs fabricated on the same wafer structure.

Surface modification of ZnO film by hydrogen peroxide solution

The effect of hydrogen peroxide (H2O2) treatment on the microstructure and luminescent properties of ZnO thin films has been investigated. Governed by high-resolution transmission electron microscopy and selected-area electron diffraction patterns, the oxygen radicals dissociated from H2O2 solution at room temperature and substantially changed the polycrystalline ZnO film into an insulator. In addition, the photoluminescence spectra showed that H2O2 solution had nearly no effect on the intensity of ultraviolet emission, whereas it significantly enhanced the intensity of deep-level emission. These observations strongly reveal the fact that the oxygen radicals penetrating into a ZnO film are reasonably speculated to occupy the interstitial sites to form oxygen interstitials Oi or fill the Zn vacancies to form antisite oxygen OZn defects. Because of these extra defects involved, an enhancement of the green light luminescence is significantly promoted in our ZnO samples after handling with H2O2 solution. Base...

Quality optimization of liquid phase deposition SiO2 films on gallium arsenide

Abstract For liquid phase deposition (LPD) at room temperature (∼40°C) of silicon dioxide (SiO 2 ) on gallium arsenide (GaAs) substrate, this study correlates growth solution concentrations with resultant film quality. This LPD process pretreats the GaAs substrate with ammonia solution kept at pH=11–12, thereby generating OH radicals on the GaAs surface which enhance SiO 2 deposition. It is found that growth conditions such as low hydrofluosilic acid concentration, proper boric acid concentration, and low growth rate play important roles in optimizing deposited film quality. When LPD-SiO 2 /GaAs grown at optimum conditions is used to fabricate a metal-oxide-semiconductor field effect transistor, the transconductance, g m , is about 68, the drain current, I DS , is 10 mA for gate oxide thickness=20 nm and W / L =40/2. LPD-SiO 2 /GaAs grown at the proposed conditions equals or exceeds the quality of competing techniques, with a process that proceeds rapidly at room temperature and pressure, with inexpensive equipment.

Effects of pH Values on the Kinetics of Liquid-Phase Chemical-Enhanced Oxidation of GaAs

The liquid-phase chemical-enhanced oxidation technique has been demonstrated to be an effective means of growing stable native films on GaAs. The gallium-ion-containing solution results in a fairly high oxidation rate near room temperature. The pH value of the oxidation solution appears to be a dominant factor in the kinetics of oxidation. Due to the enhancement of Ga-containing ca tions in the solution, a window of initial pH values from approximately 4.0 to 4.5 is found to be the optimum pH range for oxide growt h. The pH-incorporated mechanism provides consistent interpretations for the unusual experimental results such as etchback of oxid e thickness and increase of refractive index. In addition, the results of the pH-controlled procedure confirms the proposed role o f pH. According to secondary ion mass spectroscopy profiles, it is found that the increasing As/Ga ratio of the oxide film contributes to the increase of oxide refractive index.