Comparative Study of Silicon Nanowires Grown From Ga, In, Sn, and Bi for Energy Harvesting

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.A high density of silicon nanowires for solar cell applications was fabricated on a single crystalline silicon wafer, using low eutectic temperature metal catalysts, namely, gallium, indium, tin, and bismuth. The use of silicon nanowires is exploited for light trapping with an aim to enhance the efficiency of solar cells. Additionally, we have optimized the deposition parameters so that there is merely deposition of amorphous silicon along with the growth of silicon nanowires. Thus, it may improve the stability of silicon-based solar cells. The different catalysts used are extensively discussed with experimental results indicating stable growth and highly efficient silicon nanowires for photovoltaic applications. To test the stability, we measured the open-circuit voltage for four hours and the change in voltage was ±0.05 V. The fabrication of all-crystalline silicon solar cells was demonstrated using the conventional mature industrial manufacturing process that is presently used for the amorphous silicon solar cells. To summarize, this research compares various post-transition metals as a catalyst for the growth of nanowires discussing their properties, and such silicon nanowires can be utilized in several other applications not only limited to photovoltaic research

Solution processed lanthanum aluminate gate dielectrics for use in metal oxide-based thin film transistors

We report on ZnO-based thin-film transistors (TFTs) employing lanthanum aluminate gate dielectrics (LaxAl1-xOy) grown by spray pyrolysis in ambient atmosphere at 440 C. The structural, electronic, optical, morphological, and electrical properties of the LaxAl1-xOy films and devices as a function ofthe lanthanum to aluminium atomic ratio were investigated using a wide range of characterization techniques such as UV-visible absorption spectroscopy, impedance spectroscopy, spectroscopic ellipsometry, atomic force microscopy, x-ray diffraction, and field-effect measurements. As deposited LaAlOy dielectrics exhibit a wide band gap (6.18eV), high dielectric constant (k~16),low roughness (1.9 nm), and very low leakage currents (106, subthreshold swing of 650 mV dec-11, and electron mobility of 12 cm2 V-1 s-1

Experimental comparison of FBARs and SMRs responsitivities to mass loadings

The utilisation of thin film technology to develop film bulk acoustic resonators (FBARs) and solidly mounted resonators (SMRs), offers great potential to outperform the sensitivity and minimum detection limit of gravimetric sensors. Up to now, the choice between FBARs and SMRs depends primarily on the users' ability to design and fabricate Bragg reflectors and/or membranes, because neither of these two types of resonators has been demonstrated to be superior to the other. In the work reported here, it is shown that identically designed FBARs and SMRs resonating at the same frequency exhibit different responsitivities, Rm, to mass loadings, being the FBARs more responsive than the SMRs. For the specific device design and resonant frequency (~2 GHz) of the resonators presented, FBARs' mass responsitivity is ~20% greater than that of SMRs, and although this value should not be taken as universal for all possible device designs, it clearly indicates that FBAR devices should be favoured over SMRs in gravimetric sensing applications

Rotating inclined cylinder and the effect of the tilt angle on vortices

We study numerically some possible vortex configurations in a rotating cylinder that is tilted with respect to the rotation axis and where different numbers of vortices can be present at given rotation velocity. In a long cylinder at small tilt angles the vortices tend to align along the cylinder axis and not along the rotation axis. We also show that the axial flow along the cylinder axis, caused by the tilt, will result in the Ostermeier-Glaberson instability above some critical tilt angle. When the vortices become unstable the final state often appears to be a dynamical steady state, which may contain turbulent regions where new vortices are constantly created. These new vortices push other vortices in regions with laminar flow towards the top and bottom ends of the cylinder where they finally annihilate. Experimentally the inclined cylinder could be a convenient environment to create long lasting turbulence with a polarization which can be adjusted with the tilt angle.Comment: 10 pages, 10 figure

High mobility, solution processed p-type TFTs employing NiOx semiconducting channels

Despite the tremendous potential of all oxide thin film transistors for application in large area microelectronics further advancements have been hampered by the lack of hole transporting oxides with similar or comparable transport characteristics to their n-type counterparts. Although there are a few studies reporting p-type doping of traditional n-type oxides, the subject still remains controversial and stable p-type material has not been reproducibly observed. Hence, alternative metal oxides that show intrinsic p-type characteristics are required especially for applications in CMOS (complementary metal oxide semiconductor). There has been some success with alternative materials such as Cu2O and SnOx and indeed p-type TFTs were reported[1]. However TFTs incorporating Cu2O as a semiconducting channel suffer from a very low field effect mobility (< 10-2 cm2 V-1 s-1) making it unsuitable for CMOS applications. Additionally, these TFTs show high off-state currents that indicate the presence of a large number of copper vacancy defect states that pin the Fermi Level in the device. Here we report the fabrication of hole-transporting NiOx-based TFTs. Nickel nitrate hexahydrate and erythritol solutions in ethanol (0.2 M) were spin coated onto fused silica, c-Si, spray coated Al2O3 gate dielectrics and glass and underwent thermal annealing at different temperatures in air. Analyses revealed that at the optimum annealing temperature of about 340 oC NiOx films (80 nm) with optical band gap of about 3.6 eV and overall transmittance in the visible spectrum in excess of 75 % were produced. X-ray diffraction showed both cubic and hexagonal NiOx polycrystalline material (average crystal size of 15 nm) embedded in a dominant amorphous matrix. TFTs employing thermal evaporated gold source and drain contacts exhibit excellent hole transport characteristics with negligible hysteresis, low operating voltages (-10 V), high hole mobility in the order of 10 cm2 V−1 s−1 and high current on/off ratio of about 10^4. [1] P. Pattanasattayavong, S. Thomas, G. Adamopoulos, M. A. McLachlan and T. D. Anthopoulos, p-channel thin-film transistors based on spray-coated Cu2O films, Appl. Phys. Lett, 102, 163505, 201

Thin film transistors based on solution-processed In2O3:W. A remarkably stable semiconductor under high negative bias stress

A wide range of metal oxide-based semiconductors namely Indium Zinc Oxide and Indium Gallium Zinc Oxide have extensively been implemented in thin film transistors (TFTs) mainly for applications in displays. The large amount of deep defect states in Indium Zinc Oxide that are attributed to oxygen deficiency states result in TFTs instability as repeatedly reported. To tackle this issue, the inclusion of gallium has been proposed in order the oxygen deficiency states density to be reduced. It’s been evidenced however that gallium inclusion promotes device photosensitivity to visible light, an undesirable effect for applications in flat panel displays. To that end, and in order the aforementioned stability issues to be addressed we have investigated solution-processed tungsten-doped crystalline Indium Oxide (In2O3:W) as a function of the W content. In2O3:W thin films were deposited by spray coating at 350 oC in air from InCl3 and WCl5 blends in methanol and their physical properties were identified by UV-Vis absorption spectroscopy, FTIR, X-ray diffraction, AFM, and field effect measurements. For optimal deposition conditions in terms of W content, TFTs employing solution processed Al2O3 gate dielectrics, In2O3:W semiconducting channels and gold source and drain contacts underwent negative bias stress for 6000 s, and showed excellent stability characteristics such as a small change of the threshold voltage (in the range between 2 V and 2.3 V) without significantly decreasing the electron mobility, which slightly decreased from 16 to 14 cm2/Vs