Enhanced photoelectrochemical (PEC) performances of Ga(2)O(3) and GaN nanowires (NWs) grown in situ from GaN were demonstrated. The PEC conversion efficiencies of Ga(2)O(3) and GaN NWs have been shown to be 0.906% and 1.09% respectively, in contrast to their 0.581% GaN thin film counterpart under similar experimental conditions. A low crystallinity buffer layer between the grown NWs and the substrate was found to be detrimental to the PEC performance, but the layer can be avoided at suitable growth conditions. A band bending at the surface of the GaN NWs generates an electric field that drives the photogenerated electrons and holes away from each other, preventing recombination, and was found to be responsible for the enhanced PEC performance. The enhanced PEC efficiency of the Ga(2)O(3) NWs is aided by the optical absorption through a defect band centered 3.3 eV above the valence band of Ga(2)O(3). These findings are believed to have opened up possibilities for enabling visible absorption, either by tailoring ion doping into wide bandgap Ga(2)O(3) NWs, or by incorporation of indium to form InGaN NWs.
The highly porous Ti film getters on (100) silicon substrates have been successfully grown by dc magnetron sputtering with varying glancing angle. The porous films were formed when the glancing angle was higher than 30°. The larger the glancing angle, the higher the porosity and specific surface area of the Ti films. The porous films were composed of isolated columnar crystals, and they have a larger capability to absorb oxygen than dense Ti films do. Differential scanning calorimetry analysis shows that the exothermal reaction temperature for a dense Ti film is 348°C. However, that for the porous Ti film ranges from 291to394°C. The suitable operation condition of porous Ti film getters can be evaluated using thermal desorption spectroscopy. The reversible and irreversible reactions may occur during gas desorption/adsorption of porous Ti films.
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