Browsing by Author "Wu, Chih-, I"

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Angular color variation in micron-scale light-emitting diode arrays
(2019-08-05)
Yang, Shu-Mei
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Wang, Po-Hsun
;
Chao, Chia-Hsin
;
Chu, Chun-Wen
;
Yeh, Yin-Tien
A simulation scheme was developed to explore the light distribution of full-color micron-scale light-emitting diode (LED) arrays. The influences of substrate thickness, patterning, and cutting angle of the substrate on several important features, such as light field pattern, light extraction efficiency, and color variation, were evaluated numerically. An experiment was conducted; the results were consistent with simulation results for a 225 x 125 mu m(2) miniLED and those for an 80 x 80 mu m(2) microLED. Based on the simulation results, the light extraction efficiency of LED devices with a substrate increases by 67.75% over the extraction efficiency of those without a substrate. The light extraction efficiency of LED devices with a substrate increases by 113.55% when an additional patterned design is used on green and blue chips. The calculated large angle Delta u'v' can be as low as 0.015 for miniLED devices. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
Direct large-area growth of graphene on silicon for potential ultra-low-friction applications and silicon-based technologies
(2020-08-14)
Tseng, Wei-Shiuan
;
Chen, Yen-Chun
;
Hsu, Chen-Chih
;
Lu, Chen-Hsuan
;
Wu, Chih-, I
Deposition of layers of graphene on silicon has the potential for a wide range of optoelectronic and mechanical applications. However, direct growth of graphene on silicon has been difficult due to the inert, oxidized silicon surfaces. Transferring graphene from metallic growth substrates to silicon is not a good solution either, because most transfer methods involve multiple steps that often lead to polymer residues or degradation of sample quality. Here we report a single-step method for large-area direct growth of continuous horizontal graphene sheets and vertical graphene nano-walls on silicon substrates by plasma-enhanced chemical vapor deposition (PECVD) without active heating. Comprehensive studies utilizing Raman spectroscopy, x-ray/ultraviolet photoelectron spectroscopy (XPS/UPS), atomic force microscopy (AFM), scanning electron microscopy (SEM) and optical transmission are carried out to characterize the quality and properties of these samples. Data gathered by the residual gas analyzer (RGA) during the growth process further provide information about the synthesis mechanism. Additionally, ultra-low friction (with a frictional coefficient similar to 0.015) on multilayer graphene-covered silicon surface is achieved, which is approaching the superlubricity limit (for frictional coefficients <0.01). Our growth method therefore opens up a new pathway towards scalable and direct integration of graphene into silicon technology for potential applications ranging from structural superlubricity to nanoelectronics, optoelectronics, and even the next-generation lithium-ion batteries.
The photonic properties of micro/mini LED arrays with different substrate thickness
(2020-01-01)
Yang, Shu-Mei
;
Wang, Po-Hsun
;
Chao, Chia-Hsin
;
Chu, Chun-Wen
;
Chen, Yu-Sheng
In this study, we review our progress in micro/mini LED arrays and their numerical simulation in optical fields. The variation in substrate thickness will be included in the calculation and the results can provide detailed insight for the optimization of the micro/mini LED structures.