Browsing by Author "Tsai, M. T."

Now showing 1 - 2 of 2

Improved output power of GaN-based ultraviolet light-emitting diodes with sputtered AlN nucleation layer
(2015-03-15)
Chiu, C. H.
;
Lin, Y. W.
;
Tsai, M. T.
;
Lin, B. C.
;
Li, Z. Y.
In this work, the ultraviolet light emitting diodes (UV -LEDs) at 380 no were grown on patterned sapphire substrate (PSS) by atmospheric pressure metal organic chemical vapor deposition (AP-MOCVD). A sputtered AlN nucleation layer was utilized on the PSS to enhance the quality of the epitaxial layer. By using high resolution X-ray diffraction, the full width at half maximum of the rocking curve shows that the UV-LEDs with sputtered AlN nucleation layer had better crystalline quality when compared to conventional GaN nucleation samples. From the scanning electron microscope (SEM) and transmission electron microscopy (TEM) images, it can be observed that the Lip and sidewall portion of the pattern was smooth using the sputtered AlN nucleation layer. The threading dislocation densities (TDDs) are reduced from 6 x 107 cm(-2) to 2.5 x 107 cm(-2) at the interface between the u-GaN layers for conventional and AlN PSS devices, respectively. As a result, a much higher light output povver was achieved. The light output power at an injection current of 20 mA was enhanced by 30%. Further photoluminescence (PL) measurement and numerical simulation confirm that this increase or output power can be attributed to the improvement of material quality and light extraction. (C) 2014 Elsevier B.V. All rights reserved.
Microstructure and elastic modulus evolution of TiTaNb alloys
(2018-10-01)
Wei, T. Y.
;
Huang, J. C.
;
Chao, Chih-Yeh
;
Wei, L. L.
;
Tsai, M. T.
In order to develop Ti based alloys with promising biocompatibility and matching mechanical response wit} human bone, TiTaNb alloys with 15, 23 and 30 mass% Ta are designed and systematically examined in terms 01 microstructural evolution and mechanical response. The Ti-30mass%Ta-10mass%Nb is demonstrated to be sa tisfactory with an elastic modulus similar to 60 GPa, hardness similar to 3.1 GPa, and strength similar to 1250 MPa. The evolution trenc of the resulting microstructure and phases as a function of Ta content and annealing temperature are established The relationship between the various phase amounts and alloy moduli is explored.