Fang-Hsing Wang

Deposition of F-doped ZnO transparent thin films using ZnF2-doped ZnO target under different sputtering substrate temperatures.

Highly transparent and conducting fluorine-doped ZnO (FZO) thin films were deposited onto glass substrates by radio-frequency (RF) magnetron sputtering, using 1.5 wt% zinc fluoride (ZnF2)-doped ZnO as sputtering target. Structural, electrical, and optical properties of the FZO thin films were investigated as a function of substrate temperature ranging from room temperature (RT) to 300°C. The cross-sectional scanning electron microscopy (SEM) observation and X-ray diffraction analyses showed that the FZO thin films were of polycrystalline nature with a preferential growth along (002) plane perpendicular to the surface of the glass substrate. Secondary ion mass spectrometry (SIMS) analyses of the FZO thin films showed that there was incorporation of F atoms in the FZO thin films, even if the substrate temperature was 300°C. Finally, the effect of substrate temperature on the transmittance ratio, optical energy gap, Hall mobility, carrier concentration, and resistivity of the FZO thin films was also investigated.

Annealing effects of Au nanoparticles on the surface-plasmon enhanced p-Si/n-ZnO nanorods heterojunction photodetectors

The effects of various annealing temperatures (350–550 °C) of Au nanoparticles (NPs) on the surface-plasmon enhanced p-Si/n-ZnO nanorods (NRs) heterojunction photodetectors (HPDs) have been investigated. The photoresponse of the surface-plasmon-mediated HPDs was found to be determined by the extinction band of the Au NPs, the defects of ZnO NRs, and the Schottky-barrier height (SBH) between the Au and ZnO interface. The higher annealing temperature (550 °C) causes more defects in ZnO NRs and lowers the ultraviolet (UV) response of the fabricated p-Si/n-ZnO NRs HPDs. The higher annealing temperature also renders a rougher surface in the Au NPs, thereby leading to destructive interference and hence the narrowest extinction band. In contrast, the modest temperature (450 °C) results in fewer defects in ZnO NRs, the widest extinction band in Au NPs, and the lowest SBH at the Au/ZnO interface. Such a result enhances the UV-to-visible rejection ratio from 439.6 to 6447 as compared to the HPDs without Au NPs. A b...

Optical and Electrical Properties of the Different Magnetron Sputter Power 300°C Deposited -ZnO Thin Films and Applications in p-i-n -Si:H Thin-Film Solar Cells

A compound of ZnO with 3 wt% Ga2O3 (ZnO : Ga2O3 = 97 : 3 in wt%, GZO) was sintered at C as a target. The GZO thin films were deposited on glass using a radio frequency magnetron sputtering system at C by changing the deposition power from 50 W to 150 W. The effects of deposition power on the crystallization size, lattice constant (c), resistivity, carrier concentration, carrier mobility, and optical transmission rate of the GZO thin films were studied. The blue shift in the transmission spectrum of the GZO thin films was found to change with the variations of the carrier concentration because of the Burstein-Moss shifting effect. The variations in the optical band gap () value of the GZO thin films were evaluated from the plots of , revealing that the measured value decreased with increasing deposition power. As compared with the results deposited at room temperature by Gong et al., (2010) the C deposited GZO thin films had apparent blue shift in the transmission spectrum and larger value. For the deposited GZO thin films, both the carrier concentration and mobility linearly decreased and the resistivity linearly increased with increasing deposition power. The prepared GZO thin films were also used as transparent electrodes to fabricate the amorphous silicon thin-film solar cells, and their properties were also measured.

Using the Surface Plasmon Resonance of Au Nanoparticles to Enhance Ultraviolet Response of ZnO Nanorods-Based Schottky-Barrier Photodetectors

Surface plasmon resonance mediated by Gold (Au) nanoparticles (NPs) was employed to enhance the ultraviolet (UV) response of ZnO nanorod (NR)-based Schottky-barrier photodetectors (SB-PDs). The defect-level emissions of ZnO NRs induce surface plasmon resonance in Au NPs and enhance the electromagnetic field near Au NPs, which excites a great deal of electrons from Au NPs crossing over the barrier height of Au NP/ZnO interface. This causes the band-to-band emission of ZnO (384 nm) is increased by a magnitude of three, and the deep-level emissions (450-700 nm) are drastically decreased as compared to ZnO NRs without coverings of Au NPs. Also, it drastically enhances the UV (340 nm)-to-visible (560 nm) rejection ratio from 115 to 443. The effect of surface plasmon resonance is verified by that the responsivity of SB-PD with the covering of Au NPs exhibits a greater increasing with applied reverse-bias voltage than that without Au NPs.

Effects of Hydrogen on the Optical and Electrical Characteristics of the Sputter-Deposited Al2O3-Doped ZnO Thin Films

In this study, AZO thin films were deposited on glass by using a 98mol% ZnO + 1mol% Al 2 O 3 (AZO, Zn : Al = 98 : 2) ceramic target and a r.f. magnetron sputtering system. At first, the effects of different H 2 flow rates (H 2 /(H 2 + Ar) = 0%∼9.09%, abbreviated as H 2 -deposited AZO thin films, deposition temperature was 200C) added during the deposition process on the physical and electrical properties of AZO thin films were investigated. The optical transmittance at 400 nm∼700 nm is more than 80% for all AZO thin films regardless of H 2 flow rate and the transparency ratio decreased as the H 2 flow rate increased. The Burstein-Moss shift effect was used to prove that the defects of AZO thin films decreased with increasing H 2 flow rate. Also, the 2% H 2 -deposited AZO thin films were also treated by the H 2 plasma at room temperature for 60min (plasma-treated AZO thin films). The value variations in the optical band gap (E g ) values of the H 2 -deposited and plasma-treated AZO thin films were evaluated from the plots of (αh])2 = c(h] − E g ), and the E g values increased with increasing H 2 flow rate. The E g values also increased as the H 2 -plasma process was used to treat on the H 2 -deposited Al 2 O 3 -doped ZnO (AZO) thin films.

Developing high-transmittance heterojunction diodes based on NiO/TZO bilayer thin films

In this study, radio frequency magnetron sputtering was used to deposit nickel oxide thin films (NiO, deposition power of 100 W) and titanium-doped zinc oxide thin films (TZO, varying deposition powers) on glass substrates to form p(NiO)-n(TZO) heterojunction diodes with high transmittance. The structural, optical, and electrical properties of the TZO and NiO thin films and NiO/TZO heterojunction devices were investigated with scanning electron microscopy, X-ray diffraction (XRD) patterns, UV-visible spectroscopy, Hall effect analysis, and current-voltage (I-V) analysis. XRD analysis showed that only the (111) diffraction peak of NiO and the (002) and (004) diffraction peaks of TZO were observable in the NiO/TZO heterojunction devices, indicating that the TZO thin films showed a good c-axis orientation perpendicular to the glass substrates. When the sputtering deposition power for the TZO thin films was 100, 125, and 150 W, the I-V characteristics confirmed that a p-n junction characteristic was successfully formed in the NiO/TZO heterojunction devices. We show that the NiO/TZO heterojunction diode was dominated by the space-charge limited current theory.

Gate-All-Around Poly-Si TFTs With Single-Crystal-Like Nanowire Channels

The gate-all-around (GAA) poly-Si thin-film transistors (TFTs) with single-crystal-like nanowire (NW) channels (SCLNCs) are demonstrated and characterized. Via the nanoscale nitride spacer, the Si NW can be easily transformed within one crystalline grain of the two-shot sequential-lateral-solidification poly-Si film. As compared with the planar ones, the GAA-SCLNC TFTs showed more excellent characteristics. The results clearly show that the variations of device characteristics can be reduced by increasing the numbers of NWs in the channels and an average mobility above 410 cm2/V·s with a low standard deviation can be achieved for the GAA-SCLNC TFTs with 20-NW channels.

Investigation of the Structural, Electrical, and Optical Properties of the Nano-Scale GZO Thin Films on Glass and Flexible Polyimide Substrates

In this study, Ga2O3-doped ZnO (GZO) thin films were deposited on glass and flexible polyimide (PI) substrates at room temperature (300 K), 373 K, and 473 K by the radio frequency (RF) magnetron sputtering method. After finding the deposition rate, all the GZO thin films with a nano-scale thickness of about 150 ± 10 nm were controlled by the deposition time. X-ray diffraction patterns indicated that the GZO thin films were not amorphous and all exhibited the (002) peak, and field emission scanning electron microscopy showed that only nano-scale particles were observed. The dependences of the structural, electrical, and optical properties of the GZO thin films on different deposition temperatures and substrates were investigated. X-ray photoemission spectroscopy (XPS) was used to measure the elemental composition at the chemical and electronic states of the GZO thin films deposited on different substrates, which could be used to clarify the mechanism of difference in electrical properties of the GZO thin films. In this study, the XPS binding energy spectra of Ga2p3/2 and Ga2p1/2 peaks, Zn2p3/2 and Zn2p1/2 peaks, the Ga3d peak, and O1s peaks for GZO thin films on glass and PI substrates were well compared.

Physical properties of ZnO thin films codoped with titanium and hydrogen prepared by RF magnetron sputtering with different substrate temperatures

Transparent conducting titanium-doped zinc oxide (TZO) thin films were prepared on glass substrates by RF magnetron sputtering using 1.5 wt% TiO2-doped ZnO as the target. Electrical, structural, and optical properties of films were investigated as a function of H2/(Ar + H2) flow ratios (RH) and substrate temperatures (TS). The optimal RH value for achieving high conducting TZO:H thin film decreased from 10% to 1% when TS increased from RT to 300°C. The lowest resistivity of 9.2 × 10-4 Ω-cm was obtained as TS = 100°C and RH = 7.5%. X-ray diffraction patterns showed that all of TZO:H films had a hexagonal wurtzite structure with a preferred orientation in the (002) direction. Atomic force microscopy analysis revealed that the film surface roughness increased with increasing RH. The average visible transmittance decreased with increasing RH for the RT-deposited film, while it had not considerably changed with different RH for the 300°C-deposited films. The optical bandgap increased as RH increased, which is consistent with the Burstein-Moss effect. The figure of merits indicated that TS = 100°C and RH = 7.5% were optimal conditions for TZO thin films as transparent conducting electrode applications.

Multicolor Polymer Disperse Microencapsulated Liquid Crystal Displays

This work develops a new technology to fabricate polymer-dispersed microencapsulated liquid crystal (PDMLC) devices using screen-printing, which is a low temperature procedure (about 90degC) for application on a soft plastic substrate. This research demonstrates numerically and in Mandarin, a 4.5-in multicolor PDMLC (MPDMLC) device with high color contrast, low electric consumption and flexible bending mechanical property. The current work coats three different color pastes (red, blue and black) on a single substrate. Their turn-on voltages are all as low as 5 V and saturation voltages are 20, 30, and 30 V for red, blue, and black colors, respectively.