[en] Zinc sulfide (ZnS) thin films with nano-scale grains of about 50 nm were deposited on glass substrates at a substrate temperature of 200 deg. C via RF reactive sputtering by using zinc plate target and hydrogen sulfide gas. The structure, compositions, electrical and optical characteristics of the deposited films were investigated for the photovoltaic device applications. All films showed a near stoichiometric composition as indicated in their AES data. Distinct single crystalline phase with preferential orientation along the (0 0 0 1) plane of wurtzite or the (1 1 1) plane of zinc blende (ZB) was revealed in their X-ray diffraction (XRD) patterns, and the spacing of the planes are well matched to those of (1 1 2) plane of the chalcopyrite CuInS₂ (CIS). UV-Vis measurement showed that the films had more than 65% transmittance in the wavelength larger than 350 nm, and the fundamental absorption edge shifted to shorter wavelength with the increase of sulfur incorporated in the films, which corresponds to an increase in the energy band gap ranging from 3.59 to 3.72 eV. It was found that ZnS films are suitable for use as the buffer layer of the CIS solar cells, and it is the viable alternative for replacing CdS in the photovoltaic cell structure

[en] An innovative hydrogenated amorphous silicon (a-Si:H) p-i-n photodiode based X-ray detector for medical imaging applications was developed in this work, and the improvements of the device were also discussed. The detector consists of an a-Si:H p-i-n photodiode and a stacked dielectric layer, such as silicon nitride (SiN_x), deposited on p-layer of this p-i-n diode (n-i-p-SiN_x), as the major charge storage element. The detector operates as a capacitor, formed by this dielectric layer, in parallel with a reverse-biased p-i-n diode during the detection cycle. Consequently, the capacitance, for accumulating the photon-converted charges, of the p-i-n diode was enlarged by this stacked dielectric layer without decreasing the active area of the detector. As a result, the dynamic range, linearity and data retention capability of this novel detector are significantly improved. In particular, the photo sensitivity and charge storage capability of this novel detector can be separately optimized, and the drastically improved data retention, due to the high density and long release time of the trapped electrons in p-layer of the p-i-n diode, could facilitate this novel detector to be employed in the low dosage flux and long exposure applications

[en] Metal-oxide-semiconductor capacitors that incorporate ZrO₂ gate dielectrics were fabricated by radio frequency magnetron sputtering. In this work, the essential structures and electrical properties of ZrO₂ thin films were investigated. C-V, energy dispersive x-ray spectrometry, and transmission electron microscopy analyses reveal that an interfacial layer was formed, subsequently reducing the k value of the annealed ZrO₂ thin films. Additionally, the mechanisms of conduction of the Al/ZrO₂/p-Si metal/zirconium oxide/semiconductor structure were studied with reference to plots of standard Schottky emission, modified Schottky emission, and Poole-Frenkel emission. According to those results, the dominant mechanisms at high temperatures (>425 K) are Poole-Frenkel emission and Schottky emission in low electric fields (<0.6 MV/cm) and high electric fields (>1 MV/cm), respectively. Experimental results indicate that the Al/ZrO₂ barrier height is 0.92 eV and the extracted trap level is about 1.1 eV from the conduction band of ZrO₂. The modified Schottky emission can be applied in an electric field to ensure that the electronic mean free path of the insulator is less than its thickness. According to the modified Schottky emission model, the extracted electronic mobility of ZrO₂ thin films is around 13 cm²/V s at 475 K. The mean free path of transported electrons in ZrO₂ thin films is between 16.2 and 17.4 nm at high temperatures (425-∼475 K)