Browsing by Author "Yu, Tzu-Yi"

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Hydrogen etching of GaN and its application to produce free-standing GaN thick films
(2011-10-15)
Yeh, Yen-Hsien
;
Chen, Kuei-Ming
;
Wu, Yin-Hao
;
Hsu, Ying-Chia
;
Yu, Tzu-Yi
This work investigates the morphology of GaN etched in hydrogen (H(2)) at different temperatures, the activation energies of the rate-limiting steps of H(2) etching, and the overgrowth on a H(2)-etched GaN template. The surfaces of GaN have different profiles after being etched in H(2); they resemble a plane decorated with columns and mooring posts in a low-temperature etching condition, and with deep cavities in a high-temperature etching condition. The etched profiles show that H(2) etching has controllable etching directions: vertical and lateral. In a low-temperature condition, H(2) etching has both vertical and lateral etching directions; however, in a high-temperature condition, it has only the vertical etching direction. The activation energies of the rate-limiting steps under etching pressures of 100 and 700 Torr are estimated to be 3.22 and 3.77 eV, respectively. A thick GaN layer has been grown on a H2-etched GaN template, and it has self-separated from the underlying sapphire substrate. (C) 2011 Elsevier B.V. All rights reserved.
Investigations of Electro-hydrothermally Grown ZnO Nanostructures on Copper Grids
(2017-01-01)
Yu, Tzu-Yi
;
Hung, Chen Hao
;
Lee, Yu Shan
;
Lin, Chia Feng
;
Su, Wei Min
Two types of ZnO nanostructures were electro-hydrothermally deposited on mesh 100 and 200 copper grids. To investigate the nanostructures, multiple material analyses were used to analyze the material properties. FESEM images indicate that nanoflowers/nanorods could be grown on the mesh 100 copper grids while a single layer of ZnO nanorods could be grown on the mesh 200 copper grids. Since the size of the grid holes might influence the chemical reactions during the growth of the nanostructures, all the other material analyzes also reveale1 distinct material characteristics of these two types of nanostructures on the copper grid. Based on the experimental results, modulating the ZnO nanostructure will be helpful for future applications of ZnO nanostructures on copper substrates.
Use of hydrogen etching to remove existing dislocations in GaN epitaxial layers
(2015-08-01)
Yeh, Yen-Hsien
;
Chu, Chung-Ming
;
Wu, Yin-Hao
;
Hsu, Ying-Chia
;
Yu, Tzu-Yi
In this paper, based on the anisotropic nature of hydrogen (H-2) etching on GaN, we describe a new approach to the removal of threading dislocations in GaN layers. The top surfaces of c-plane (Ga-face) and a-plane GaNs are considered stable in H-2; therefore, H-2 etches only crystal imperfections such as dislocation and basal plane stacking fault (BSF) sites. We used H-2 to etch undoped c-plane GaN, n-type c-plane GaN, a-plane GaN, and an InGaN/ GaN multiple quantum well structure. Several examinations were performed, indicating deep cavities on the c-plane GaN samples after H-2 etching; furthermore, gorge-like grooves were observed on the a-plane GaN samples. The deep cavities on the c-plane GaN were considered the etched dislocation sites, and the gorge-like grooves on the a-plane GaN were considered the etched BSF sites. Photoluminescence measurements were performed and the results indicated that the H-2-etched samples demonstrate superior optoelectronic properties, probably because of the elimination of dislocations.
ZnO nanoflakes on silver wires with antibacterial effects
(2016-05-01)
Huang, Shen-Che
;
Hsieh, Kun Min
;
Chang, Ting Wei
;
Chen, Yi Cian
;
Yu, Chang-Tze Ricky
ZnO structures were electro-hydrothermally grown on copper and silver wires. To characterize the structures, multiple analyses including field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction and photoluminescence measurements were performed on the ZnO structures on the wires. Results indicate that ZnO nanoflakes were densely deposited on the silver wire but poor ZnO structures were grown on the copper wire. Furthermore, OD 600 antibacterial tests revealed that ZnO flakes on the silver wire exhibited better antibacterial capability than the silver wire without ZnO nanoflakes. Because of possible integration with silver-related materials and flexibility of wire structures, ZnO nanoflake-coated silver wires have potentials for future antiseptic and biomedical applications. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.