In this paper the current transport mechanism of ZnO-based metal-semiconductor-metal ultraviolet photodetectors with various contact electrodes is discussed and simulated. The simulation is based on the thermionic emission theory and tunneling effects. It was found that the lowest dark current attributes to the Ru contact electrode. Moreover, it is shown that in order to achieve a large Schottky barrier height on ZnO and more reduction of dark current, one can insert a thin oxide layer between contacts and ZnO layer. The influence of the thickness of the insulator layer on the dark current of the MIS photodetector has also analyzed.
[Show abstract][Hide abstract] ABSTRACT: We report the fabrication of ZnO-based metal–insulator–semiconductor (MIS) and metal–semiconductor–metal (MSM) photodetectors. With 5 V applied bias, it was found that photocurrent to dark current contrast ratios of the ZnO MSM and MIS photodetectors were 2.9 × 10 2 and 3.2 × 10 4 , respectively. It was also found that measured responsivities were 0.089 and 0.0083 A/W for the ZnO MSM and MIS photodetectors, respectively, when the incident light wavelength was 370 nm. Furthermore, it was found that ultraviolet (UV) to visible rejection ratios for the fabricated ZnO MSM and MIS photodetectors were 2.4 × 10 2 and 3.8 × 10 3 , respectively.
Sensors and Actuators A Physical 04/2007; 7860(85). DOI:10.1016/j.sna.2006.10.001 · 1.90 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: ZnO epitaxial films were grown on sapphire substrates by molecular beam epitaxy. Schottky diodes and metal–semiconductor–metal (MSM) photodetectors with ruthenium (Ru) electrodes were also fabricated. It was found that Schottky barrier height at the Ru/ZnO interface was 0.76eV. It was also found that we achieved a photocurrent to dark current contrast ratio of 225 from our ZnO MSM photodetectors. Furthermore, it was found that the time constant of our photodetectors was 13ms with three-order decay exponential function.
[Show abstract][Hide abstract] ABSTRACT: A multistep pulsed-laser deposition (PLD) process is presented for epitaxial, nominally undoped ZnO thin films of total thickness of 1 to 2 mum on c-plane sapphire substrates. We obtain reproducibly high electron mobilities from 115 up to 155 cm2/V s at 300 K in a narrow carrier concentration range from 2 to 5×1016 cm-3. The key issue of the multistep PLD process is the insertion of 30-nm-thin ZnO relaxation layers deposited at reduced substrate temperature. The high-mobility samples show atomically flat surface structure with grain size of about 0.5-1 mum, whereas the surfaces of low-mobility films consist of clearly resolved hexagonally faceted columnar grains of only 200-nm size, as shown by atomic force microscopy. Structurally optimized PLD ZnO thin films show narrow high-resolution x-ray diffraction peak widths of the ZnO(0002) omega- and 2Theta-scans as low as 151 and 43 arcsec, respectively, and narrow photoluminescence linewidths of donor-bound excitons of 1.7 meV at 2 K.
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