Browsing by Author "Lai, Yung-Yu"

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Annealed Polycrystalline TiO2 Interlayer of the n-Si/TiO2/Ni Photoanode for Efficient Photoelectrochemical Water Splitting
(2020-04-27)
Chuang, Chi-Huang
;
Lai, Yung-Yu
;
Hou, Cheng-Hung
;
Cheng, Yuh-Jen
;
材料科學與工程學系
High photovoltage generation from a photoelectrode is important for efficient solar-driven water splitting. Here, we report a thermal treatment process that greatly enhances photovoltage generation from an n-Si/TiO2/Ni photoanode. By selectively annealing the TiO2 interlayer, the photoanode generates a high photovoltage of 570 mV, which is very competitive as compared with photovoltages produced using other similar metal-insulator-semiconductor structures with earth-abundant metal catalysts. Different annealing conditions and junction layer thicknesses were systematically investigated. It is found that the optimal annealing temperature occurs between 500 and 600 degrees C. Within this temperature range, the deposited amorphous Ti is converted into polycrystalline anatase phase TiO2. The optimal annealing time scales linearly with TiO2 thickness and inversely with annealing temperature. The large photovoltage generation is attributed to the reduced defect states and improved junction barrier height by the annealed TiO2 interlayer. This study demonstrates that thermal annealing offers an attractive approach to modify the TiO2 interlayer material's properties for photovoltage optimization.
Self-assembled InN growth on GaN nanorod
(2014)
Chang, Shih-Pang
;
Lai, Yung-Yu
;
Cheng, Yuh-Jen
;
Han, Jung
;
Kuo, Hao-Chung
We report a self-assembled InN epitaxial growth on GaN nanorods. Crystalline InN hexagonal structure was selectively grown on the sidewall edges of GaN hexagonal nanorods. The growth mechanism and the photoluminescent property will be discussed.
Site-controlled crystalline growth of InN on GaN substrate and its photoluminscence
(2016)
Kuo, Chien-Ting
;
Hsu, Lung-Hsing
;
Lai, Yung-Yu
;
Kuo, Hao-Chung
;
Lin, Chien-Chung
We report a site-controlled growth of InN on a GaN substrate. Crystalline InN micropillars were selectively grown from the hexagonal V-pits on GaN surface. The grown mechanism and photoluminescent property will be discussed.
Site-controlled crystalline InN growth from the V-pits of a GaN substrate
(2017-05-31)
Kuo, Chien-Ting
;
Hsu, Lung-Hsing
;
Lai, Yung-Yu
;
Cheng, Shan-Yun
;
Kuo, Hao-Chung
A site-controlled crystalline InN growth from the V-pits of a GaN substrate was investigated. The V-pits were fabricated by epitaxial lateral growth of GaN over SiO2 disks patterned on a sapphire substrate. InN crystals were found to preferably grow on the inclined {10-11} crystal planes of the V-pits. A V-pit size of 1 mu m or less can provide precise site-controlled InN nucleation at the V-pit bottom, while no InN was grown on the rest of the exposed GaN surfaces. The site-controlled nucleation is attributed to the low surface energy point created by the converging six {10-11} crystal facets at the V-pit bottom. When In source supply is below a certain value, this V-pit bottom is the only location able to aggregate enough active sources to start nucleation, thereby providing site-controlled crystal growth. (C) 2017 Elsevier B.V.
The study of wet etching on GaN surface by potassium hydroxide solution
(2017-06-01)
Lai, Yung-Yu
;
Hsu, Shih-Chieh
;
Chang, Hua-Sheng
;
Wu, YewChung Sermon
;
Chen, Ching-Hsiang
Potassium hydroxide solution was used to etch un-doped GaN grown on the sapphire substrate at 180 and 260 A degrees C. We illustrated the etching phenomenon in detail and probed its mechanism in the wet etching process. By multiplying the planar density and the number of dangling bonds on the N atom, we proposed the etching barrier index (EBI) to describe the difficulty degree of each lattice facet. The raking of EBI will be +c-plane > a-plane > m-plane > -c-plane > (10-1-1) plane > r-plane. Combining the EBI with SEM results, we thoroughly studied the whole etching process. We confirmed that in our research, KOH wet etching on GaN starts from the r-plane instead of the +c-plane or -c-plane, which differs from other studies. We also found that during the high-temperature etching process, there are two etching approaches. In one, the etching begins vertically from the top to the bottom, then horizontally, and finally reversely from the bottom to the top. In the other, etching pits will develop into a hexagonal hole of the sidewall of m-plane.