Browsing by Author "Kuo, Shiou-Yi"

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Anti-guiding and guiding effects in GaN-based vertical-cavity surface-emitting lasers
(2020-02-01)
Chen, Lih-Ren
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Chen, Bo-Yan
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Kuo, Shiou-Yi
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Hong, Kuo-Bin
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Lu, Tien-Chang
We study the lateral optical confinement effect on the performance and lasing characteristics of GaN-based vertical-cavity surface-emitting lasers (VCSELs). The anti-guiding and guiding structures are designed by calculating the effective refractive index difference of active and cladding regions. By varying the compensation layer configuration and thickness, the designed effective refractive index of the active region is 0.44% higher than peripheral for the guiding structure. The threshold current density of VCSEL with the guiding structure is 25.4 kA/cm(2), which is almost half of that with the anti-guiding structure showing 53.5 kA/cm(2). For the anti-guiding structure, the signals from both active and cladding regions are observed by the far-field angle-resolved spectrum at 1.4 x I-th driving current, which agrees well with our simulation. Throughout the study, we show the advantage of the guiding structure both theoretically and experimentally. Moreover, an effective guiding structure is obtained by a proper design and simple device process, which will be very promising for mass production.
Enhanced Light Output of UVA GaN Vertical LEDs With Novel DBR Mirrors
(2015-12-01)
Kuo, Shiou-Yi
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Hong, Kuo-Bin
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Lu, Tien-Chang
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交大名義發表
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National Chiao Tung University
The emission efficiency of GaN-based light-emitting diodes (LEDs) decreases significantly as the emission wavelength is shorter than 370 nm because of the absorption of emission light in the GaN layers. The vertical LED structure could be applied to avoid the absorption problem, because the undoped GaN layer would be removed and the n-GaN layer could be thinned as much as possible in the fabrication process. In this report, we propose a novel ultraviolet (UV) LED structure with a thin indium-tinoxide (ITO) layer as the ohmic contact and a dielectric distributed Bragg reflector (DBR) as the high reflectivity mirror. Comparing referenced vertical UV LED structures with ITO/Ag as the metal mirror, the vertical UV LED with the ITO/DBR mirror shows the output power of approximately 190 mW at 350 mA with 7.9% enhancement.
GaN-based vertical-cavity surface-emitting lasers operating at high temperature
(2017-01-01)
Chang, Tsu-Chi
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Kuo, Shiou-Yi
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Lian, Jhen-Ting
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Hong, Kuo-Bin
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Lu, Tien-Chang
We report on GaN-based vertical-cavity surface emitting lasers (VCSELs) capable of high temperature operation. The structures of VCSELs include double dielectric distributed Bragg reflectors and bonded to a silicon substrate with a p-side-down configuration, allowing a better heat dissipation. The temperature dependent lasing characteristics of VCSELs can sustain to 350K.
High efficiency GaN-based near UV light emitting diodes with asymmetric triangular multiple quantum wells
(2018-01-01)
Li, Heng
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Chang, Chia-Jui
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Kuo, Shiou-Yi
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Chen, Jun-Rong
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Lu, Tien-Chang
Near-ultraviolet (NUV) light-emitting diodes (LEDs) have found many applications in the areas such as UV curing, bio-chemical sensors etc. However, the internal quantum efficiency (IQE) of NUV-LEDs show relatively lower value than blue LEDs. In previous research, asymmetric triangular MQWs with gallium face-oriented inclination in the blue wavelength band are demonstrated to have higher emission efficiency and lower efficiency droop. In this study, we surprisingly found different trend in NUV-LEDs. Compared to blue LEDs, NUV-LEDs tend to have shallower quantum wells and less ability to localize holes. In the simulation results, holes are more confined within nitrogen face-oriented inclination than that in MQWs with gallium face-oriented inclination and the IQE are improved about 10%.
High Output Power GaN-Based Green Resonant-Cavity Light-Emitting Diodes With Trapezoidal Quantum Wells
(2020-09-01)
Wu, Haocheng
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Li, Heng
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Kuo, Shiou-Yi
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Chen, Bo-Yan
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Lu, Tien-Chang
Green resonant-cavity light-emitting diode (RCLED) has great potential in optical communication but suffers low efficiency. In this study, GaN-based flip-chip green RCLED incorporated with nitrogen face-oriented inclination asymmetric trapezoidal quantum wells (NOAT-QWs) is proposed to enhance the light-output power (LOP). Samples with NOAT-QWs and normal symmetric square quantum wells (SS-QWs) were fabricated and characterized. Although their electrical characteristics and emission spectra are similar, the LOP and emission efficiency are significantly improved. At a driving current of 450 mA, the improvement of LOP for RCLED with NOAT-QWs can be as high as 1.44 times in comparison to the sample with SS-QWs. The unprecedented high output power of 115 mW and the narrow full-width-at-half-maximum (FWHM) of 6.4 nm in the emission spectrum give great potential in optical communication. The inherent mechanism was investigated by the finite element analysis, from which the simulation results match well with the experimental measurements. The simulation results reveal that the NOAT-QWs are beneficial in alleviating the quantum confined stark effect and facilitating easier hole carriers' flow across the barriers, leading to more electron-hole wave function overlaps and higher radiative recombination rate.
High-temperature operation of GaN-based vertical-cavity surface-emitting lasers
(2017-11-01)
Chang, Tsu-Chi
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Kuo, Shiou-Yi
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Lian, Jhen-Ting
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Hong, Kuo-Bin
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Wang, Shing-Chung
We report GaN-based vertical-cavity surface-emitting lasers (VCSELs) capable of high-temperature operation. The GaN-based VCSELs include double dielectric distributed Bragg reflectors and epitaxially grown p-i-n InGaN multiple-quantum-well active layers initially deposited on c-plane sapphire substrates that are bonded to a silicon substrate with a p-side-down and patterned mirror configuration, allowing effective heat dissipation. GaN-based VCSELs with an emission aperture 10 mu m in diameter were fabricated, and their temperature-dependent lasing characteristics revealed that the VCSELs can endure 350 K, as measured under quasicontinuous-wave operation conditions. The temperature-dependent lasing wavelength shift occurs at a rate of d lambda(FP)/dT approximate to 0.012nm/K. The high-temperature operation of GaN-based VCSELs was attributed to the well-matched gain-mode offset, the p-side-down configuration, and the reduced lateral size of the bottom distributed Bragg reflector with recessed metal. (C) 2017 The Japan Society of Applied Physics
Improved Performance of Near UV GaN-Based Light Emitting Diodes With Asymmetric Triangular Multiple Quantum Wells
(2019-02-01)
Li, Heng
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Chang, Chia-Jui
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Kuo, Shiou-Yi
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Wu, Hao-Cheng
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Huang, Huamao
Near-ultraviolet (NUV) light-emitting diodes (LEDs) have been used in several potential applications such as UV curing and biochemical sensors. However, the internal quantum efficiency (IQE) of NUV-LEDs is still a crucial issue. To improve the IQE, in this paper, an asymmetric triangular multiple quantum well (MQW) structure was used, which exhibited a higher emission efficiency and lower efficiency droop with nitrogen face-oriented inclination. This is in contrast to the trend observed in blue LEDs. Furthermore, we demonstrated that holes are more confined in MQWs with nitrogen face-oriented inclination than in MQWs with gallium face-oriented inclination. Moreover, simulations revealed that the IQE improved by approximately 32% compared with that of symmetric square MQWNUV-LEDs; this trend was also confirmed through experimental results. The external quantum efficiency of thin-film flip-chip LEDs with nitrogen face-oriented inclination MQWs was 52%.
Polarization control of GaN-based micro-caivty lasers with top high-contrast grating reflectors
(2019-01-01)
Chang, Tsu-Chi
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Hong, Kuo-Bin
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Kuo, Shiou-Yi
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Lu, Tien-Chang
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光電工程學系
We reported on GaN micro-cavity (MC) lasers combining one rigid TiO2 high-contrast grating (HCG) structure as the output mirror. HCG structure was made directly on the GaN without an airgap, designed to yield high reflectance for transverse magnetic (TM) or transverse electric (TE) polarized light. The laser emission was TM polarized with a degree of polarization of 99.2% and had a small divergence angle of 14 degrees (full width at half maximum), under pulsed optical pumping at room temperature. This demonstration of laser operation for the GaN-based MC with an HCG fully exhibited advantages of HCGs for applications in semiconductor lasers at the wavelength from green to ultraviolet regimes.