Browsing by Author "Tu, Chia-Cheng"

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Improved Output Power of InGaN-Based Ultraviolet LEDs Using a Heavily Si-Doped GaN Insertion Layer Technique
(2012-02-01)
Chiu, Ching-Hsueh
;
Lin, Chien-Chung
;
Tu, Po-Min
;
Huang, Shih-Cheng
;
Tu, Chia-Cheng
In this paper, a high quality ultraviolet lightemitting diodes (UV-LEDs) at 375 nm was developed using a heavy Si-doping technique with metal organic chemical vapor deposition. By using high-resolution X-ray diffraction, the full width at half-maximum of the rocking curve shows that the GaN film inserting a heavily Si-doped GaN layer (Si-HDL) had high crystalline quality. From the transmission electron microscopy image, the threading dislocation density was decreased after inserting a Si-HDL between undoped and n-doped GaN layers by nanoscale epitaxial lateral overgrowth. As a result, a much smaller reverse current and a higher light output were achieved. The improvement of light output at an injection current of 20 mA was enhanced by 40%. Therefore, we can use an in-situ nano pattern without complex photolithography and etching process and improve the internal quantum efficiency of UV-LEDs.
Improvement in Crystalline Quality of InGaN-Based Epilayer on Sapphire via Nanoscaled Epitaxial Lateral Overgrowth
(2010)
Chiu, Ching-Hsueh
;
Lin, Da-Wei
;
Li, Zhen-Yu
;
Chiu, Chin-Hua
;
Chao, Chu-Li
In this study, a high-performance GaN-based light-emitting diode (LED) was achieved using a nanocolumn patterned sapphire substrate (NCPSS) with low-pressure metal-organic chemical vapor deposition (LP-MOCVD). The surface roughness was evaluated by atomic force microscopy (AFM). The mechanisms of carrier localization in the GaN-based LED fabricated on NCPSS were discussed referring to the results obtained from the power-dependent photoluminescence measurements. Moreover, from the transmission electron microscopy (TEM) image, the threading dislocation densities (TDDs) through the GaN-based LED fabricated on NCPSS were found to be about 10 times lower than those fabricated on planar substrates. Finally, the internal quantum efficiency (IQE) of the GaN-based LED fabricated on NCPSS was as high as 48% at 30 mW, corresponding to a current of 20 mA, which is higher than that of a GaN-based LED fabricated on a planar sapphire substrate by 8%. The use of NCPSS is suggested to be effective for elevating the emission efficiency of the GaN-based LED owing to an improvement in crystal quality. (C) 2010 The Japan Society of Applied Physics
Study of 375 nm ultraviolet InGaN/AlGaN light-emitting diodes with heavily Si-doped GaN transition layer in growth mode, internal quantum efficiency, and device performance
(2011-12-15)
Huang, Shih-Cheng
;
Shen, Kun-Ching
;
Wuu, Dong-Sing
;
Tu, Po-Min
;
Kuo, Hao-Chung
High performance 375 nm ultraviolet (UV) InGaN/AlGaN light-emitting diodes (LEDs) were demonstrated with inserting a heavy Si-doped GaN transition layer by metal-organic chemical vapor deposition. From transmission electron microcopy (TEM) image, the dislocation densities were significantly reduced due to the existence of the heavily Si-doping growth mode transition layer (GMTL), which results in residual stress relaxation and 3D growth. The internal quantum efficiency (IQE) of the LEDs with GMTL was measured by power-dependent photoluminescence (PL) to be 40.6% higher than ones without GMTL. The GMTL leads to the superior IQE performance of LEDs not only in decreasing carrier consumption at nonradiative recombination centers but also in partially mitigating the efficiency droop tendency. When the vertical-type LED chips (size: 1 mm x 1 mm) was driven with a 350 mA injection current, the output powers of the LEDs with and without GMTL were measured to be 286.7 and 204.2 mW, respectively. A 40.4% enhancement of light output power was achieved. Therefore, using the GMTL to reduce dislocations would be a promising prospective for InGaN/AlGaN UV-LEDs to achieve high IQE. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3669377]