Bohr-Ran Huang

Nitride-based light-emitting diodes with Ni/ITO p-type ohmic contacts

The optical and electrical properties of Ni(5 nm)-Au(5 nm) and Ni(3.5 nm)-indium tin oxide (ITO) (60 nm) films were studied. It was found that the normalized transmittance of Ni/ITO film could reach 87% at 470 nm, which was much larger than that of the Ni-Au film. It was also found that the specific contact resistance was 5 /spl times/ 10/sup -4/ /spl Omega/ /spl middot/ cm/sup 2/ and 1 /spl times/ 10/sup -3/ /spl Omega/ /spl middot/ cm/sup 2/, respectively, for Ni-Au and Ni/ITO on p-GaN. Furthermore, it was found that the 20 mA output power of light-emitting diode (LED) with Ni-Au p-contact layer was 5.26 mW. In contrast, the output power could reach 6.59 mW for the LED with Ni/ITO p-contact layer.

Highly Sensitive ZnO Nanowire Acetone Vapor Sensor With Au Adsorption

In this study, the growth of high-density single-crystalline ZnO nanowires on patterned ZnO:Ga/ SiO2/Si templates was reported. We also adsorbed Au onto nanowire surfaces and fabricated ZnO nanowire acetone vapor sensors. With 200-ppm acetone vapor concentration, it was found that we could enhance the device sensitivities at 300deg C from 18.5% to 82.5% by Au adsorption. It was also found that measured responses at 300degC were around 52%, 61%, 71%, 77%, and 82% when the accumulative acetone vapor concentration reached 5, 10, 50, 100, and 200 ppm, respectively, for the ZnO nanowire sensor with Au adsorption.

Photo-CVD SiO/sub 2/ layers on AlGaN and AlGaN-GaN MOSHFET

High-quality SiO/sub 2/ was successfully deposited onto AlGaN by photochemical vapor deposition (photo-CVD) using a D/sub 2/ lamp as the excitation source. The resulting interface state density was only 1.1 /spl times/ 10/sup 11/ cm/sup -2/eV/sup -1/, and the oxide leakage current was dominated by Poole-Frenkel emission. Compared with AlGaN-GaN metal-semiconductor HFET (MESHFETs) with similar structure, the gate leakage current is reduced by more than four orders of magnitude by using the photo-CVD oxide layer as gate oxide in AlGaN-GaN metal-oxide-semiconductor heterojunction field-effect transistors (MOSHFETs). With a 2-/spl mu/m gate, the saturated I/sub ds/, maximum g/sub m/ and gate voltage swing (GVS) of the fabricated nitride-based MOSHFET were 572 mA/mm, 68 mS/mm, and 8 V, respectively.

ZnSe Nanowire Photodetector Prepared on Oxidized Silicon Substrate by Molecular-Beam Epitaxy

We reported the growth of ZnSe nanowires on oxidized Si substrate by molecular-beam epitaxy. It was found that average length, average diameter, and density of the ZnSe nanowires were 1.2 μm, 48 nm, and 1.04 X 10 7 cm -2 , respectively. It was also found that the ZnSe nanowires were structurally uniform and defect-free with a pure zinc blend structure. UV photodetectors were then fabricated by sputtering a thick Au film through an interdigitated shadow mask onto the ZnSe nanowires. It was found that photocurrent to dark current contrast ratio of our ZnSe nanowire photodetector was >90 with 0.1 V applied bias.

ZnO Branched Nanowires and the p-CuO/n-ZnO Heterojunction Nanostructured Photodetector

The authors report the growth of ZnO branched nanowires on the CuO nanowires and the fabrication of p-CuO/n-ZnO heterojunction nanostructured photodetector (PD). It was found that the hydrothermally grown ZnO branched nanowires were reasonably uniform with an average length of 200 nm and an average diameter of 50 nm. Under forward bias, it was found that turn on voltage of the fabricated PD reduced from ~0.7 to ~0.2 V under ultraviolet (UV) illumination. It was also found that UV-to-visible rejection ratio of the fabricated device was larger than 100.

Deposition of SiO2 Layers on GaN by Photochemical Vapor Deposition

SiO 2 insulating layers were first deposited onto GaN by photochemical vapor deposition (photo-CVD) technology using a deuterium (D 2 ) lamp as the excitation source. Physical, chemical, and electrical characteristics of the Al/SiO 2 /GaN metal-insulator-semiconductor (MIS) capacitors are reported for the first time. It was also found that the limiting factor of SiO 2 growth rate was the number of SiH 4 and O 2 molecules available to provide excited Si and O atoms. Furthermore, it was found from high-frequency capacitance-voltage measurements that the photo-CVD SiO 2 /n-GaN interface state density. D it , was estimated to be 8.4 × 10 11 cm -2 eV -1 for the photo-CVD SiO 2 layers prepared at 300°C. With an applied field of 4 MV/cm. the oxide leakage current density was found to he only 6.6 × 10 -7 A/cm 2 .

CuO Nanowire-Based Humidity Sensor

The authors report the growth of CuO nanowires on an oxidized Cu wire and the fabrication of a CuO nanowire humidity sensor. It was found that we could transform a Cu wire into CuO/Cu2O/Cu core-shell tri-layers covered with high density CuO nanowires by thermal annealing. It was also found that steady state currents of the sensor were about 2.44, 2.32, 2.23, and 2.15 μA , respectively, when measured with 20, 40, 60, and 80% relative humidity. Furthermore, it was found that sensing property of the fabricated device was stable and reproducible.

A unified analytical fully depleted and partially depleted SOI MOSFET model

In this paper we present a unified analytical drain current model for fully depleted and partially depleted SOI MOSFETs. The analytical model is based on a nonpinned surface potential approach and is valid in all regions of operation. It was developed by starting from a two-dimensional Poisson equation, and its accuracy has been verified with the experimental data of SOI MOSFETs.

Leaf-like carbon nanotube/nickel composite membrane extended-gate field-effect transistors as pH sensor

A leaf-like carbon nanotube/nickel (CNT/Ni) composite nanostructure is used as the sensing membrane in an extended-gate field-effect transistor (EGFET) for the pH sensors is first developed using nanocomposite plating technique. While sensing pH within a range of 2-10, the leaf-like CNT/Ni EGFET exhibits a sensitivity of 59 mV/pH. This simple and low-cost sensing membrane can be applied in disposable biosensors.

ZnSe homoepitaxial MSM photodetectors with transparent ITO contact electrodes

We report the homoepitaxial growth of ZnSe layers on ZnSe substrates by molecular beam epitaxy (MBE). It was found that we can only observe an extremely strong ZnSe (004) x-ray peak with a full-width-at-half-maximum of 21.5 arcsec, which is much smaller than that observed from ZnSe grown on GaAs substrates. Photoluminescence and Hall measurement also indicate that the quality of our homoepitaxial ZnSe layers is good. ZnSe-based homoepitaxial metal-semiconductor-metal photodetectors with transparent indium-tin-oxide (ITO) contact electrodes were also fabricated. It was found that although ITO transparent contact electrodes can result in large photon absorption and large photocurrents, the low Schottky barrier height between ITO and homoepitaxial ZnSe would also result in relatively large dark currents. With an incident wavelength of 450 nm and a 1-V applied bias, it was found that the maximum responsivity is about 0.13 A/W, which corresponds to a quantum efficiency of 35%. Furthermore, it was found that the detector responsivity drops by more than two orders of magnitude across the cutoff region.