Browsing by Author "Lee, Wei-I."

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Controlling bottom-up rapid growth of single crystalline gallium nitride nanowires on silicon
(2017-12-20)
Wu, Ko-Li
;
Chou, Yi
;
Su, Chang-Chou
;
Yang, Chih-Chaing
;
Lee, Wei-I.
We report single crystalline gallium nitride nanowire growth from Ni and Ni-Au catalysts on silicon using hydride vapor phase epitaxy. The growth takes place rapidly; efficiency in time is higher than the conventional nanowire growth in metal-organic chemical vapor deposition and thin film growth in molecular beam epitaxy. The effects of V/III ratio and carrier gas flow on growth are discussed regarding surface polarity and sticking coefficient of molecules. The nanowires of gallium nitride exhibit excellent crystallinity with smooth and straight morphology and uniform orientation. The growth mechanism follows self-assembly from both catalysts, where Au acts as a protection from etching during growth enabling the growth of ultra-long nanowires. The photoluminescence of such nanowires are adjustable by tuning the growth parameters to achieve blue emission. The practical range of parameters for mass production of such high crystal quality and uniformity of nanowires is suggested.
Homoepitaxy on GaN substrate with various treatments by metalorganic vapor phase epitaxy
(2011-03-01)
Chen, Kuei-Ming
;
Wu, Yin-Hao
;
Yeh, Yen-Hsien
;
Chiang, Chen-Hao
;
Chen, Kuei-You
This study shows the morphological, optical, and crystal characteristics of homoepitaxial GaN epilayers that were overgrown by metalorganic vapor phase epitaxy (MOVPE) on the Ga-polar face of GaN substrates that had undergone various surface treatments. The MOVPE overgrown epilayer with surface treatment was fine polished (sample C) to obtain a flat surface that exhibits two-dimensional step-flow growth. And the interface between the MOVPE overgrown epilayer and the GaN substrate was completely absent, indicating the continuous growth of GaN, and, correspondingly, the high degree of homoepitaxy. However, a network of cracks appeared in as-grown sample A (mechanically polished) and hillocks formed with the striped morphology in as-grown sample B (ICP treated). The dislocation density and full width at half maximum (FWHM) obtained by X-ray measurements of as-grown sample C were superior to those obtained by other surface treatments and the original GaN substrate. According to the photoluminescence (PL) and cathodoluminescence (CL) measurements, the decreasing FWHM of band edge emission (NBE) of the overgrown epilayers was attributable to the point defects of V(N) being greatly reduced. Additionally, cross-sectional transmission electron microscopy (TEM) revealed that many threading dislocations formed in sample A by edge type dislocations and intermittently appeared due to inter-crack. (C) 2010 Elsevier B.V. All rights reserved.