Browsing by Author "Huang, Shih-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.
Improved performance of 375 nm InGaN/AlGaN light-emitting diodes by incorporating a heavily Si-doped transition layer
(2012-01-01)
Huang, Shih-Cheng
;
Shen, Kun-Ching
;
Tu, Po-Min
;
Wuu, Dong-Sing
;
Kuo, Hao-Chung
High performance 375-nm ultraviolet (UV) InGaN/AlGaN light-emitting diodes (LEDs) was developed using a heavy Si-doping technique with metalorganic chemical vapor deposition (MOCVD). From the transmission electron microcopy (TEM) image, the dislocation density was reduced after inserting a heavily Si-doping growth mode transition layer (GMTL) between un-doped GaN layer and Si-doped Al0.02Ga0.98N contact layer. The internal quantum efficiency (IQE) of the sample with GMTL measured by power-dependent photoluminescence shows 39.4% improved compared with the sample without GMTL. When the vertical type LED chips (size: 1mmx1mm) driving by a 350-mA current, the output powers of the LEDs with and without GMTL were measured to be 286.7 mW and 204.2 mW, respectively. As much as 40.4% increased light output power was achieved. Therefore, using the GMTL to reduce dislocation defects would be a promising prospective for InGaN/AlGaN UV LEDs to achieve high internal quantum efficiency.
Investigation of efficiency droop for InGaN-based UV light-emitting diodes with InAlGaN barrier
(2011-05-23)
Tu, Po-Min
;
Chang, Chun-Yen
;
Huang, Shih-Cheng
;
Chiu, Ching-Hsueh
;
Chang, Jet-Rung
The efficiency droop in InGaN-based UV light emitting device (LED) with AlGaN and InAlGaN barrier is investigated. Electroluminescence results indicate that the light performance of quaternary LEDs can be enhanced by 25% and 55% at 350 mA and 1000 mA, respectively. Furthermore, simulations show that quaternary LEDs exhibit 62% higher radiative recombination rate and low efficiency degradation of 13% at a high injection current. We attribute this improvement to increasing of carrier concentration and uniform redistribution of carriers. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3591967]
Investigation of Efficiency Droop for UV-LED with N-type AlGaN Layer
(2012-01-01)
Tu, Po-Min
;
Chang, Jet-Rung
;
Huang, Shih-Cheng
;
Yang, Shun-Kuei
;
Lin, Ya-wen
The efficiency droop in InGaN-based 380nm UV light emitting device (LED) with n-GaN and n-AlGaN underlayer grown on sapphire substrate by metal-organic chemical vapor deposition (MOCVD) was investigated. From simulation result of high resolution x-ray diffraction (HRXRD) omega-2 theta. curve by using dynamical diffraction theory, the Al composition in the n-AlGaN layer was determined to be about 3%. The experimental results of temperature dependent photoluminescence (PL) demonstrated that the internal quantum efficiency (IQE) of n-GaN and n-AlGaN UV-LEDs are 43% and 39%, respectively, which are corresponding to an injected carrier density of 8.5 x 10(17) #/cm(3). It could be explained that the crystal quality of n-GaN is better than of n-AlGaN. In addition, the observation of pit density from atomic force microscopy (AFM) surface morphology is consistent with the interpretation. It was well-known that the pits appearing on the surface in the virtue of the threading dislocations. Thus, it means that defects induce the non-radiative centers and deteriorate the IQE of the UV-LED with n-AlGaN underlayer. Therefore, the light output power of n-GaN UV-LED is slightly higher below the forward current of 250 mA. Nevertheless, the output power was enhanced about 22% as the injection current was increased to 600 mA. Furthermore, the external quantum efficiency (EQE) of n-AlGaN UV-LED was nearly retained at the 600 mA (only 20% droop), whereas the UV-LED with n-GaN exhibits as high as 33%. We attributed this improvement to the less self-absoption by replacing n-GaN underlayer with n-AlGaN.
Investigation of Efficiency Droop in GaN-based UV LEDs with N-type AlGaN Underlayer
(2012)
Yang, Shun-Kuei
;
Tu, Po-Min
;
Huang, Shih-Cheng
;
Lin, Ya-wen
;
Hsu, Chih-Peng
The efficiency droop in InGaN-based 380nm UV light emitting device (LED) with n-GaN and n-AlGaN underlayer grown on sapphire substrate by metal-organic chemical vapor deposition (MOCVD) was investigated. From simulation result of high resolution x-ray diffraction (HRXRD) omega-2 theta curve by using dynamical diffraction theory, the Al composition in the n-AlGaN layer was determined to be about 3%. The experimental results of temperature dependent photoluminescence (PL) demonstrated that the internal quantum efficiency (IQE) of n-GaN and n-AlGaN UV-LEDs are 43% and 39%, respectively, which are corresponding to an injected carrier density of 8.5 x 10(17) #/cm(3). It could be explained that the crystal quality of n-GaN is better than of n-AlGaN. In addition, the observation of pit density from atomic force microscopy (AFM) surface morphology is consistent with the interpretation. It was well-known that the pits appearing on the surface in the virtue of the threading dislocations. Thus, it means that defects induce the non-radiative centers and deteriorate the IQE of the UV-LED with n-AlGaN underlayer
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]
Study of Efficiency Droop in InGaN-based Near-UV LEDs with Quaternary InAlGaN Barrier
(2012)
Tu, Po-Min
;
Huang, Shih-Cheng
;
Lin, Ya-wen
;
Yang, Shun-Kuei
;
Hsu, Chih-Peng
In this study, we demonstrate high efficient near-UV LEDs by replacing low-temperature AlGaN by InAlGaN barrier in active region. The efficiency droop in InGaN-based near-UV LED with AlGaN and InAlGaN barrier is investigated. High-resolution x-ray diffraction (HRXRD) and transmission electron microscopy (TEM) measurements show the two barriers are consistent with the lattice, and smooth morphology of quaternary InAlGaN layer can be observed in atomic force microscopy (AFM). Electroluminescence results indicate that the light performance of quaternary LEDs can be enhanced by 25 % and 55 % at 350 mA and 1000mA, respectively. Furthermore, simulations show that quaternary LEDs exhibit 62 % higher radiative recombination rate and low efficiency degradation of 13 % at a high injection current. We attribute this improvement to increasing of carrier concentration and more uniform redistribution of carriers.