Yueh-Hsun Lee

Al-Doped ZnO ∕ Cu2O Heterojunction Fabricated on (200) and (111)-Orientated Cu2O Substrates

Heterojunction devices were fabricated and composed of Al-doped ZnO films deposited by radio-frequency magnetron sputtering on Cu 2 O films with different orientation obtained by potentiostatic electrodeposition. Compared to the Al-doped ZnO/(200)-orientated Cu 2 O heterojunction, regardless of the intentional substrate heating during the deposition of Al-doped ZnO, the Al-doped ZnO/(111)-orientated Cu 2 O heterojunction has an epitaxy-like growth for Al-doped ZnO films due to a small lattice mismatch of about 7.1%. With the substrate heating, the resistance of the device increases, although the crystallinity of Al-doped ZnO films could be improved. The device composed of Al-doped ZnO/(111)-orientated Cu 2 O without substrate heating has the best photovoltaic characteristics and the highest conversion efficiency of 0.069% under the illumination condition of AM1.5 in this study. In addition, by modifying the thickness of the heterojunction, the best conversion efficiency of the Al-doped ZnO(200 nm)/(111)-orientated Cu 2 O (1 μm) heterojunction could be promoted to 0.22% with a short-circuit current (J SC ) of 4.3 mA/cm 2 , an open-circuit voltage (V OC ) of 0.15 V, and a fill factor of 0.29.

The role of solidus velocity in the feeding behaviour of Al7si0.3Mg alloy plate castings

Abstract The present study attempts to investigate systematically the combined influence of feeder size and casting length on the feeding behaviour of Al7Si0.3Mg alloy. The castings were examined by X-ray radiography and density measurement to determine their feeding efficiency. During solidification, thermal data were taken to analyse the thermal gradient G, the local solidification time t, the ratio G/t and the solidus velocity V S . The purpose was to characterize the significance of the solidus velocity compared with other parameters in predicting the formation of porosity. The solidus velocity is proposed as a useful parameter to characterize the feeding of Al7Si0.3Mg alloy in which measurement of the thermal gradient at the final stage of solidification becomes difficult. Both riser size and length of casting exert a large influence on the solidus velocity from the free end to the riser. The solidus velocity is slow at the free end; it increases to a maximum at a position about one-third of the distance from the riser end and then slows down again when approaching the riser. Good prediction of V S on porosity content is obtained in this experiment.