| Summary: | 碩士 === 國立成功大學 === 微電子工程研究所碩博士班 === 95 === In this thesis, electrical and optical properties of Ru contact on n-type ZnO epitaxial layers were investigated. 100-nm-thick Ru films were deposited onto n-ZnO epitaxial layers by rf sputtering. It was found hat highly transparent RuOx was form after O2 annealing. With an incident wavelength of 460 nm, it was found that transmittances of as-grown, 500 oC-annealed, 600 oC-annealed and 700 oC-annealed Ru films were 56.8 %, 73.5 %, 79.6 % and 86.8 %, respectively. In addition, it was also found that as-deposited Ru formed Schottky contact on n-ZnO. However, good ohmic contacts were formed between the annealed Ru films and the underneath ZnO. With 650oC-annealing, we achieved a specific contact resistance of only 2.72x10e-4 Ω-cm2. Such a low specific contact resistance should be attributed to the formation of RuOx and the dissociation of oxygen atoms in ZnO during annealing.
Moreover, ZnO photoconductive sensor was also fabricated and characterized. We report the fabrication of ZnO photoconductive sensors epitaxially grown on sapphire substrates with interdigitated Ni/Au electrodes. It was found that there exists an electric field dependent photoconductive gain in the fabricated sensors. With an incident light wavelength of 365 nm and an applied electric field of 500 V/cm, it was found that maximum responsivity and quantum efficiency were respectively around 54 mA/W and 2.8 % while time constant of the decay transient was τ~0.556 ms. In addition, with a 5 V applied bias, it was found that NEP and normalized detectivity of the fabricated sensors were 1.83×10e-6 W and 6.91x10e5 cmHz0.5W-1, respectively.
In addition, ZnO/GaN heterojunction light emitting diode was also fabricated and characterized. We have detailed the growth, processing, and fabrication of an n-ZnO/p-GaN heterojunction light emitting diode on a c-Al2O3 substrate, and characterized the electroluminescence from this device. Diode-like I–V characteristics and RT electroluminescent (EL) spectrum with intense broadband-emission in the yellow-green region has been observed under forward bias. Photoluminescent (PL) and Raman spectra of the p-ZnO and n-GaN films were also measured. By comparing PL and EL spectra, it is concluded that the deep-level defect-emission emerged mainly from the GaN epitaxial layer.
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