Ying-Nan Lai

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 .

Magnetoelectronic Properties of a Single-Layer Graphite

The magnetoelectronic structure of a single-layer graphite is mainly determined by the strength, the period, and the direction of the modulated magnetic field. Such field could induce the destruction of state degeneracy, the drastic change of energy dispersion, the increment of band-edge states, and the alternation of band width. Most of energy bands become nondegenerate, and the flat bands are replaced by the parabolic bands. Density of states exhibits the linear energy dependence, the square-root divergences, the logarithmic divergences, the discontinuous structures, and the delta-function-like divergences. These special structures directly reflect rich energy spectra.

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.

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.

Efficiency Improvement of Organic Solar Cell with Metal Anode by Using Wet Oxidation

In this work, the approaches to improve the organic solar cell with metal anode are studied. Under the hydrogen peroxide and ozone water treatment, the work function and surface roughness of metal anode are varied and hence to affect the fill factor (F.F.) and photocurrent of organic solar cells. By using hydrogen peroxide with diluted ratio of 1:70, the power conversion efficiency of the organic solar cell is increased from 0.34% to 0.81%. Under the ozone water treatment by 6 sec., the power conversion efficiency is increased from 0.34% to 0.99%.