Sheng-Joue Young

Ultraviolet photodetectors based on selectively grown ZnO nanorod arrays

Metal-semiconductor-metal (MSM) ultraviolet (UV) photodetectors with ZnO nanorods (NRs) have been fabricated and characterized in this investigation. The NR arrays were selectively grown on the gap of interdigitated electrodes by chemical solution method through a photolithography process. Compared to a traditional ZnO MSM photodetector with no NRs, the fabricated NR UV photodetector showed much higher photoresponsity. As a result, it can be attributed to high surface-to-volume ratio of ZnO NRs and such a high photoresponse could strongly depend on oxygen adsorption/desorption process in the presence of trap states at the NR surface.

Buckling characterization of vertical ZnO nanowires using nanoindentation

Nanomechanical characterization of vertical well-aligned single-crystal ZnO nanowires on ZnO:Ga/glass templates was performed by nanoindentation technique. The buckling loads were found to be 1465 and 215μN for the ZnO nanowires of 100 and 30nm diameters, respectively. Furthermore, the buckling energies for the ZnO nanowires of 100 and 30nm diameters were 3.62×10−10 and 3.69×10−11J, respectively. Based on the Euler buckling model, Young’s modulus of the individual ZnO nanowire has been derived from two possible modes in this work.

Nanoscale mechanical characteristics of vertical ZnO nanowires grown on ZnO:Ga/glass templates

The mechanical properties of vertical single-crystal ZnO nanowires on ZnO:Ga/glass templates were characterized by nanoindentation experiments in this work. The results from x-ray diffraction and Raman spectra show good crystal quality for the ZnO nanowires. The buckling loads were found to be 1465 and 215 μN for ZnO nanowires of 100 and 30 nm diameters, respectively. When the fixed‐fixed column mode was used, it was found that the Young’s modulus values of the ZnO nanowires of 100 and 30 nm diameters were 117 and 232 GPa, while the critical buckling strains were 0.62% and 0.35%, respectively. On the other hand, when we employed the fixed‐pinned column mode, it can be seen that the Young’s modulus values were 229 and 454 GPa, while the critical buckling strains were 0.32% and 0.18%, respectively. Buckling behaviour of the ZnO nanowires was significantly predicted by the Euler buckling model in this work.

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.

Characterization of ZnO metal–semiconductor–metal ultraviolet photodiodes with palladium contact electrodes

ZnO metal–semiconductor–metal (MSM) photodiodes with palladium (Pd) contact electrodes were fabricated. It was found that the barrier height at the Pd/ZnO interface was 0.701 eV. With an incident wavelength of 370 nm and 1 V applied bias, it was found that the maximum responsivity of the Pd/ZnO/Pd MSM photodiodes was 0.051 A/W, which corresponds to a quantum efficiency of 11.4%. For a given bandwidth of 100 Hz and 1 V applied bias, we found that the noise equivalent power and the corresponding detectivity D ∗ were 1.13 × 10 −12 W and 6.25 × 10 11 cmHz 0.5 W −1 , respectively.

TiO2-Based Thin Film Transistors with Amorphous and Anatase Channel Layer

In this study, TiO 2 films were deposited on FTO (fluorine-doped tin oxide)/glass substrate by radio frequency magnetron sputtering. Amorphous and anatase structure of TiO 2 were achieved without and with thermal process, respectively. Further, TiO 2 -based thin-film transistors (TFTs) with different structure were fabricated. After the electrical characteristics measurement, it was found that the amorphous TiO 2 TFTs can be operated in the enhancement mode with a threshold voltage of 3.8 V. It was also found that the field-effect mobility and on/off current of the TiO 2 TFT with amorphous channel layer were 0.087 cm 2 V ―1 s ―1 and 10 3 , respectively. On the other hand, the TiO 2 TFTs with anatase structure were also tested. It was found that the anatase TiO 2 TFTs have the lower threshold voltage of 2.3 V than amorphous one. Besides, it was also found that the field effect mobility and on/off current ratio of the anatase TiO 2 TFTs were both increased to 10.7 cm 2 V ―1 s ―1 and 10 4 , respectively. In other words, the performance of TiO 2 TFTs was related to the structure of the channel layer.

Bending effects of ZnO nanorod metal–semiconductor–metal photodetectors on flexible polyimide substrate

The authors report the fabrication and I-V characteristics of ZnO nanorod metal–semiconductor–metal photodetectors on flexible polyimide substrate. From field-emission scanning electron microscopy and X-ray diffraction spectrum, ZnO nanorods had a (0002) crystal orientation and a wurtzite hexagonal structure. During the I-V and response measurement, the flexible substrates were measured with (i.e., the radius of curvatures was 0.2 cm) and without bending. From I-V results, the dark current decreased, and the UV-to-visible rejection ratio increased slightly in bending situation. The decreasing tendency of the dark current under bending condition may be attributed to the increase of the Schottky barrier height.

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.

ZnO Schottky diodes with iridium contact electrodes

Schottky diodes with iridium (Ir) contact electrodes on ZnO films were fabricated and characterized in this work. The Schottky barrier height between Ir and ZnO was determined to be 0.824 ± 0.04%, 0.837 ± 0.04% and 0.924 ± 0.04% eV by the thermionic emission model, the Norde model and capacitance–voltage measurement, respectively. It was also found that the ideality factor of the fabricated ZnO-based Schottky diode was 1.68.

UV Enhanced Emission Performance of Low Temperature Grown Ga-Doped ZnO Nanorods

We report on hydrothermal growth and gallium doping of ZnO (GZO) nanorods for field emitters. The GZO nanorods grown at 90°C were structurally uniform and well oriented with pure wurtzite structure. It was also found that turn-on fields were 5.4 and 3.6 V/μm while field-enhancement factors β were 1711 and 9058, for the ZnO nanorods and GZO nanorods grown at 90°C, respectively. In addition, the turn-on electrical field was reduced from 3.6 to 3.15 V/μm and β of GZO nanorods was enhanced from 9058 to 13529 by UV illumination.