Chiu-Sheng Ho

Novel Oxide-Passivated AlGaN/GaN HEMT by Using Hydrogen Peroxide Treatment

This brief reports, for the first time, an oxide passivated AlGaN/GaN high electron mobility transistor by using the hydrogen peroxide (H2O2) treatment. Characterizations by using electron spectroscopy for chemical analysis and transmission electron microscopy have been performed to verify the formation of surface oxide on the AlGaN barrier layer. The present design has demonstrated superior improvements of 41% in the maximum drain/source current density IDS,max; 39% in the drain/source saturation current density at zero gate bias IDSSO, 47% in the maximum extrinsic transconductance gm,max, 53.2% in the two-terminal gate/drain breakdown voltage BVGD 36% in the cutoff frequency fT, and 20% in the maximum oscillation frequency fmax, as compared with an unpassivated conventional device.

A Simple Gate-Dielectric Fabrication Process for AlGaN/GaN Metal–Oxide–Semiconductor High-Electron-Mobility Transistors

This letter reports a simple processing method for fabricating metal-oxide-semiconductor high-electron-mobility transistors (MOS-HEMTs) by using hydrogen peroxide (H₂O₂) oxidation technique. Aluminum oxide (AlO_x) was formed on the surface of the AlGaN barrier as the gate dielectric of the MOS-gate structure. By using the capacitance-voltage measurement, the dielectric constant (κ) of AlO_x was determined to be 9.2. The present MOS-HEMT has demonstrated enhanced saturation drain current density at V_GS = 0 V (I_DSS0) of 552.3 mA/mm, maximum extrinsic transconductance (g_{m, max}) of 136 mS/mm, wide gate voltage swing of 2.9 V, and two-terminal gate-drain breakdown/turn-on voltages (BV_GD/V_on) of -132.2/1.82 V.

Investigations of AlGaN/AlN/GaN MOS-HEMTs on Si Substrate by Ozone Water Oxidation Method

Al_0.3Ga_0.7N/AlN/GaN metal-oxide-semiconductor high electron mobility transistors (HEMTs) grown on Si substrates by using ozone water oxidation method are investigated. Superior improvements of 52.2% in two-terminal gate-drain breakdown voltage (BV_GD), 30.3% in drain-source current density (I_DS) at V_GS = 0 V (I_DSS0), 43.6% in maximum I_DS (I_DS,max), 34.7% in maximum extrinsic transconductance (<i>gm</i>,max), and 52.7%/34.3% in unity-gain cutoff/maximum oscillation frequency (<i>fT</i>/<i>f</i>_max) are achieved as compared with a reference Schottky-gated HEMT. Thermal stability is studied by conducting temperature-dependent characterizations of devices at ambient temperatures of 300-550 K. Time-dependent electrical reliability analyses for the devices stressed in off-state (V_GS = -20 V and V_DS = 0 V) for 0-60 h and on-state (V_GS = 2 V and V_DS = 20 V) for 0-20 h are also made to physically investigate the dominant degradation mechanisms. Excellent reliability and thermal stability at 300-550 K are achieved by the present design.

Comparative studies of MOS-gate/oxide-passivated AlGaAs/InGaAs pHEMTs by using ozone water oxidation technique

Al0.22Ga0.78As/In0.24Ga0.76As pseudomorphic high-electron-mobility transistors (pHEMTs) with metal-oxide-semiconductor (MOS)-gate structure or oxide passivation by using ozone water oxidation treatment have been comprehensively investigated. Annihilated surface states, enhanced gate insulating property and improved device gain have been achieved by the devised MOS-gate structure and oxide passivation. The present MOS-gated or oxide-passivated pHEMTs have demonstrated superior device performances, including superior breakdown, device gain, noise figure, high-frequency characteristics and power performance. Temperature-dependent device characteristics of the present designs at 300–450 K are also studied.

Effects of Annealing on Polymer Solar Cells with High Polythiophene–Fullerene Concentrations

The effects of annealing at high temperatures on polymer solar cells consisting of conjugated poly(3-hexylthiophene) (P3HT) and fullerene derivative [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) composites with high concentrations of 3 and 5 wt % are reported. As compared with as-casted samples, the optical intensity in absorption spectra for the 3 wt % film was improved after annealing at temperatures of 110–150 °C, and the device made of 5 wt % blend film after annealing at 150 °C demonstrated nearly sevenfold improvements in both short-circuit current density (Jsc) and power conversion efficiency (PCE).

InAlAs/InGaAs MOS-MHEMTs by Using Ozone Water Oxidation Treatment

This article reports an InAlAs/InGaAs metal oxide semiconductor metamorphic high electron mobility transistor (MOS-MHEMT) by using ozone water oxidation treatment to form an 8.5 nm thick gate oxide with a superior surface flatness. The proposed MHEMT with (without) ozone treatment has demonstrated a lower gate leakage density of 2 μA/mm (0.48 mA/mm) at V gd = -5 V, improved output conductance (g d ) of 8.5 (33.1) mS/mm, gate-voltage swing of 0.9 (0.45) V, enhanced output power of 18.34 (13.43) dBm, and power-added efficiency of 46.8 (26.3)% at 300 K, with gate dimensions of 1 × 200 μm 2 .

Efficiency Improvement of Top-Emission Organic Light Emitting Diode by Using UV-Ozone, Doped Emission Layer, and Hole-Blocking Layer

This work investigates systematic approaches to improve the current efficiency of the devised top-emission organic light emitting diode (TOLED) with a UV-ozone-treated reflective Ag anode, doped emission layer, and hole-blocking layer. The work function of the Ag anode can be increased under the UV-ozone exposure to improve the current density-voltage property of TOLED. Yet, degraded sheet resistance and reflectance characteristics of the Ag anode are observed. Therefore, a trade-off to obtain optimum performance of the studied TOLED is investigated. Besides, structural design by doping 2,3,6,7-tetrahydro-1,1,7,7,-tetramethyl-1H,5H,11H-10-(2-benzothiazolyl)quinolizino-[9,9a,1gh]coumarin into the emission layer to improve the carrier recombination efficiency to obtain enhanced current efficiency is also studied.

Investigations on In0.45Al0.55As/InxGa1-xAS Metamorphic High-Electron-Mobility Transistors with Double Gate-Recess and SiNx Passivation

Comparative investigations on linearly graded In 0.45 Al 0.55 As/In x Ga 1-x AS (x = 0.53 → 0.63) metamorphic high-electron-mobility transistors (MHEMTs) with/without applying SiN x surface passivation or double-gate-recess techniques have been comprehensively made in this work. The proposed double-gate-recessed, SiN x -passivated MHEMT with gate dimensions of 0.65 X 200 μm 2 has demonstrated superior extrinsic transconductance (g m,max ) of 445 mS/mm, gate-drain breakdown voltage of - 13.1 V, intrinsic voltage gain of 69, saturated output power of 14.33 dBm (135 mW/mm), and power-added efficiency of 53.8%, due to its enhanced gate-modulation capability, suppressed gate leakages, and relieved kink effects. The proposed device can be promisingly applied to high-gain and high-power millimeter-wave integrated circuit technologies.

An Alternative Approach for Improving Performance of Organic Photovoltaics by Light-Enhanced Annealing

This work proposes an approach for improving the performance of poly(3-hexylthiophene) (P3HT-) based organic photovoltaics (OPVs). P3HT-based bulk heterojunction (BHJ) film can absorb the energy from 532 nm laser light and be transformed into favorable morphology. A combination of traditional thermal annealing and laser annealing improved device performance, with a slight increase in fill factor and a significant improvement in short-circuit current density. Better crystallization and a higher degree of molecular order in the thermal/laser coannealed P3HT-based BHJ film were observed through X-ray diffraction and Raman spectroscopy.

Performance Improvement in Poly(3-hexylthiophene):[6,6]-Phenyl C61 Butyric Acid Methyl Ester Polymer Solar Cell by Doping Wide-Gap Material Tris(phenylpyrazole)iridium

This letter demonstrates the high external quantum efficiency (EQE) of poly(3-hexylthiophene) (P3HT)-based polymer solar cells and their enhanced hole transport ability through doping a wide-band-gap material tris(phenylpyrazole)iridium [Ir(ppz)3]. Doping Ir(ppz)3 can enhance low wavelength optical absorption capacity and doping a small amount of Ir(ppz)3 can also improve the crystallinity of P3HT. Moreover, the large energy barrier between Ir(ppz)3 and the polymer active layer, which can reduce the electron current densities and increase the hole current densities, indicates a more balanced carrier transport based on hole- and electron-only devices. Such characteristics contribute to efforts to improve the photocurrent density of polymer solar cells.