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Ohmic Contact Fabrication Using a Focused-ion Beam Technique and Electrical Characterization for Layer Semiconductor Nanostructures

Layer semiconductors with easily processed two-dimensional (2D) structures exhibit indirect-to-direct bandgap transitions and superior transistor ...

National Taiwan University of Science and Technology

Photoconductivities of monocrystalline vanadium pentoxide (V2O5) nanowires (NWs) with layered orthorhombic structure grown by physical vapor deposition (PVD) have been investigated from the points of view of device and material. Optimal responsivity and gain for single-NW photodetector are at 7,900 A W-1 and 30,000, respectively. Intrinsic photoconduction (PC) efficiency (i.e., normalized gain) of the PVD-grown V2O5 NWs is two orders of magnitude higher than that of the V2O5 counterpart prepared by hydrothermal approach. In addition, bulk and surface-controlled PC mechanisms have been observed respectively by above- and below-bandgap excitations. The coexistence of hole trapping and oxygen sensitization effects in this layered V2O5 nanostructure is proposed, which is different from conventional metal oxide systems, such as ZnO, SnO2, TiO2, and WO3.

Photoconductivities in monocrystalline layered V2O5 nanowires grown by physical vapor deposition.

We report the optoelectronic device properties of individual Au-silica hybrid nanowires prepared by microwave plasma enhanced chemical vapor deposition. Due to the surface plasmon resonance (SPR) effect the photo-responsivity peak strongly depends on the shape of the embedded gold nanostructures in the silica nanowire in which the shape can be modified by controlling the growth time of Au-silica nanowires. Finite difference time domain (FDTD) simulation shows that the electric field distribution profiles of Au-silica hybrid nanowires support the photo-responsivity spectrum results. The photodetector performance of the Au-NPs@silica nanowire is investigated. The single Au-NPs@silica nanowire exhibits unique photo-responsivity in the visible range (500 nm), high selectivity, high photoconductive gain, and very fast rise (141 μs) and decay (298 μs) time constants. Furthermore, the mechanism for the high photoconductive gain is also discussed. This result implies that the Au-NPs@silica nanowire can be applied for future nanoscale optoelectronic devices.

Surface plasmon resonance-induced color-selective Au-peapodded silica nanowire photodetectors with high photoconductive gain.

We report on the observation of the substantial thickness (t)-dependent electrical conductivity (σ) at a wide thickness range for an MoSe₂ layer semiconductor. The conductivity increases for more than two orders of magnitude from 4.6 to 1500 Ω(-1) cm(-1) with a decrease in thickness from 2700 to 6 nm. The conductivity was found to follow a nearly linear relationship with the reciprocal thickness, i.e. σ ∝ 1/t. The temperature-dependent conductivity measurements also show that the MoSe₂ multilayers have much lower activation energies at 3.5-8.5 meV than those (36-38 meV) of their bulk counterparts, indicating the different origins of the majority carrier. These results imply the presence of higher surface conductivity or carrier surface accumulation in this layer crystal. The fabrication of ohmic contacts for the MoSe₂ layer nanocrystals using the focused-ion beam (FIB) technique was also demonstrated. This study provides a new understanding which is crucial for the development of flexible electronic devices and transparent conducting materials using ultrathin dichalcogenide layer materials.

Article	Year
Photoconductivities in monocrystalline layered V2O5 nanowires grown by physical vapor deposition. Nanoscale research letters\| PubMed ID: 24160337	2013
Surface plasmon resonance-induced color-selective Au-peapodded silica nanowire photodetectors with high photoconductive gain. Nanoscale\| PubMed ID: 24326397	2014
Thickness-dependent electrical conductivities and ohmic contacts in transition metal dichalcogenides multilayers. Nanotechnology\| PubMed ID: 25249412	2014

Ruei-San Chen

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