Browsing by Author "Lu, Tien-Chang"

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3D Finite Element Strain Analysis of V-Shaped Pits in Light Emitting Diodes
(2015)
Hsu, Chung-Cheng
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Wu, Chen-Kuo
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Li, Chi-Kang
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Lu, Tien-Chang
;
Wu, Yuh-Renn
In this paper, we have analyzed the strain distribution of the V-pits in light emitting diodes (LEDs). The special geometry and non-uniform distribution introduce the complicated strain and piezoelectric distribution, where it might affect the carrier injection. In the future, we will combine the calculated piezoelectric field with our in-house developed 3D drift-diffusion model to figure out how the carrier inject into LEDs with V-pits.
3D numerical modeling of the carrier transport and radiative efficiency for InGaN/GaN light emitting diodes with V-shaped pits
(2016-05-01)
Li, Chi-Kang
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Wu, Chen-Kuo
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Hsu, Chung-Cheng
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Lu, Li-Shuo
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Li, Heng
In this paper, influence of a V-pit embedded inside the multiple quantum wells (MQWs) LED was studied. A fully three-dimensional stress-strain solver and Poisson-drift-diffusion solver are employed to study the current path, where the quantum efficiency and turn-on voltage will be discussed. Our results show that the hole current is not only from top into lateral quantum wells (QWs) but flowing through shallow sidewall QWs and then injecting into the deeper lateral QWs in V-pit structures, where the V-pit geometry provides more percolation length for holes to make the distribution uniform along lateral MQWs. The IQE behavior with different V-pit sizes, threading dislocation densities, and current densities were analyzed. Substantially, the variation of the quantum efficiency for different V-pit sizes is due to the trap-assisted nonradiative recombination, effective QW ratio, and ability of hole injections. (C) 2016 Author(s).
3D structural construction of GaN-based light emitting diode by confocal micro-Raman spectroscopy
(2016-01-01)
Li, Heng
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Chang, Chiao-Yun
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Cheng, Hui-Yu
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Chen, Wei-Liang
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Huang, Yi-Hsin
The key issue for light emission strength of GaN-based LEDs is the high defect density and strain in MQWs causing the electric polarization fields. In this work, we construct 3D confocal microspectroscopy to clarify strain distribution and the relationship between photoluminescence (PL) intensity and pattern sapphire substrate (PSS). From 3D construction of E-2(high) Raman and PL mapping, the dislocation in MQW can be traced to the cone tip of PSS and the difference in E-2(high) Raman mapping between substrate and surface is also measured. The ability to measure strain change in 3D structure nondestructively can be applied to explore many structural problems of GaN-based optoelectronic devices.
830-nm AlGaAs-InGaAs Graded Index Double Barrier Separate Confinement Heterostructures Laser Diodes With Improved Temperature and Divergence Characteristics
(2013-01-01)
Hung, Chih-Tsang
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Lu, Tien-Chang
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光電工程學系
;
Department of Photonics
The 830-nm AlGaAs/InGaAs laser diodes (LDs) adopting multistep-graded index double-barrier separate confinement heterostructures (GRIN-DBSCHs) with small divergence beams and improved temperature characteristics under a high-output-power operation are reported. The double-barrier separate confinement heterostructure (DBSCH) design provides good carrier confinement and prevents current leakage by adding a multistep grading layer between cladding and waveguide layers. Simultaneously, the DBSCH design can facilitate reducing the divergence angle at high-power operation and widening the transverse mode distribution to decrease the power density around emission facets. In addition, the p-side doping depth is optimized to effectively raise the barrier height for reducing the electron overflow. Gaussian-like narrow far-field patterns are measured with the full-width at half-maximum vertical divergence angle to be between 11 degrees and 13 degrees. A threshold current of 16.5 mA and a slop efficiency of 0.98 W/A are obtained in the continuous-wave operation condition at room temperature. The maxima optical power densities of 21.5 MW/cm(2) per laser facet and good characteristic temperature values of threshold current (T-0) and slope efficiency (T-1) are achieved.
830nm Graded Index Double Barrier Separate Confinement Heterostructure Laser Diodes with Small Vertical Divergence and Temperature Insensitive Characteristics
(2012)
Hung, Chih-Tsang
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Ho, Tsong-Lin
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Lu, Tien-Chang
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光電工程學系
;
Department of Photonics
Abnormal polarization switching phenomenon in a-plane Al(x)Ga(1-x)N
(2010-10-11)
Huang, Huei-Min
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Huang, Hung-Hsun
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Wu, Yuh-Renn
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Lu, Tien-Chang
;
光電工程學系
The optical polarization properties of a-plane Al(x)Ga(1-x)N films have been investigated by polarization-dependent photoluminescence (PL). The degree of polarization decreased with increasing the Al composition, and the main optical polarization direction switched from epsilon perpendicular to c to epsilon // c at about x = 0.07 due to the valence band switching, representing that the optical transition energy of epsilon // c is surpassing that of epsilon perpendicular to c. However, with the Al composition larger than x = 0.1, the higher energy optical transitions of epsilon // c exhibited the stronger PL intensity, opposite to the normal situations that higher energy states commonly have weaker PL intensity than the lower energy states. We utilized the 6 x 6 k.p model and the lambertian-like radiation pattern assumption to explain this abnormal optical polarization switching behavior in the a-plane Al(x)Ga(1-x)N layers and obtained good agreement with the experimental results. (C) 2010 Optical Society of America
Abnormal polarization switching phenomenon in a-plane Al(x)Ga(1-x)N
(2011-01-01)
Huang, Huei-Min
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Huang, Hung-Hsun
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Wu, Yuh-Renn
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Lu, Tien-Chang
;
Kuo, Hao-Chung
The a-plane Al(x)Ga(1-x)N layers show abnormal optical polarization switching behavior. This phenomenon can be well characterized by the assumption of the lambertian-like radiation pattern and simulated by utilizing the 6 x 6 k . p model. (C) 2010 Optical Society of America
Abnormal polarization switching phenomenon in a-plane AlxGa1-xN
(2010-10-11)
Huang, Huei-Min
;
Huang, Hung-Hsun
;
Wu, Yuh-Renn
;
Lu, Tien-Chang
;
照明與能源光電研究所
The optical polarization properties of a-plane AlxGa1-xN films have been investigated by polarization-dependent photoluminescence (PL). The degree of polarization decreased with increasing the Al composition, and the main optical polarization direction switched from epsilon perpendicular to c to epsilon // c at about x = 0.07 due to the valence band switching, representing that the optical transition energy of epsilon // c is surpassing that of epsilon perpendicular to c. However, with the Al composition larger than x = 0.1, the higher energy optical transitions of epsilon // c exhibited the stronger PL intensity, opposite to the normal situations that higher energy states commonly have weaker PL intensity than the lower energy states. We utilized the 6 x 6 k.p model and the lambertian-like radiation pattern assumption to explain this abnormal optical polarization switching behavior in the a-plane AlxGa1-xN layers and obtained good agreement with the experimental results. (C) 2010 Optical Society of America
Abnormal polarization switching phenomenon in a-plane AlxGa1-xN
(2011-01-01)
Huang, Huei-Min
;
Huang, Hung-Hsun
;
Wu, Yuh-Renn
;
Lu, Tien-Chang
;
Kuo, Hao-Chung
The a-plane AlxGa1-xN layers show abnormal optical polarization switching behavior. This phenomenon can be well characterized by the assumption of the lambertian-like radiation pattern and simulated by utilizing the 6 x 6 k . p model. (C) 2010 Optical Society of America
Analysis of Quality Factor Enhancement in the Monolithic InGaN/GaN Nanorod Array
(2019-04-01)
Huang, Chia-Yen
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Tai, Tzu-Ying
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Hong, Kuo-Bin
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Kuo, Hao-Chung
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Lu, Tien-Chang
Whispering gallery mode (WGM) lasers and resonators are key building blocks for photonic integrated circuits. The quality factor and resonant wavelength are strong functions of the cavity size. Nanoscale WGM cavities suffer from a low-quality factor due to prominent scattering loss. However, the quality factor could be enhanced by forming an optically-coupled rod array or photonic molecules. Through simulations, we revealed how rod-to-rod optical coupling influenced the threshold pumping level and dominant mode selection, where the trend showed good agreement with the experimental observation. According to the simulation, the quality factor could be enhanced by up to eight times by forming a six-rod photonic molecule. The quality factor and effective mode were both superior to the single rods with the same wafer device footprint.
Angular-resolved Lasing Characteristics at Different Band Edges in GaN Photonic Crystal Surface Emitting Lasers
(2010)
Chen, Shih-Wei
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Lu, Tien-Chang
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Hou, Yun-Ju
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Liu, Ting-Chun
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Kuo, Hao-Chung
We successfully demonstrated and analyzed the angular-resolved characteristics of GaN-based photonic-crystal surface emitting lasers at different band edges (Gamma, K, and M), showing specific lasing angles in measured dispersion diagram. (C) 2010 Optical Society of America
Anisotropy light extraction with high polarization ratio from photonic crystal fight-emitting diodes
(2008)
Lai, Chun-Feng
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Kuo, Hao-Chung
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Lu, Tien-Chang
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Wang, Shing-Chang
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Chao, C. H.
The azimuthal anisotropy of GaN photonic crystal light-emitting diode is investigated using an annular structure. The extracted light distribution has P/S ratio of 5.5 for fight propagating in Gamma X direction and 2.1 for Gamma M direction. @2007 Optical Society of America
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.
Antibacterial capability of ZnO-based nanostructures manipulated by flake-coated onto silver wires
(2016)
Huang, Shen-Che
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Wang, Tze-Ting
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Lu, Tien-Chang
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Chen, Hsiang
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光電工程學系
ZnO nanoscale structures were grown on the silver wire, utilizing the electro-hydrothermal method, which deposited to further grow flake-form with pellicle and floccule status via employing certain characterizations. The analysis reveals that ZnO nanoscale flake-form were successfully coated on Ag wire. Besides, the antibacterial testing of sample with ZnO nanoscale flake-form integrated on the polished silver wire may support future detection platforms.
Asymmetric design of photonic crystal surface-emitting lasers with low-threshold characteristics
(2013-08-10)
Hung, Chih-Tsang
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Ho, Tsung-Lin
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Lu, Tien-Chang
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光電工程學系
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Department of Photonics
We present AlGaAs-InGaAs multiquantum wells photonic crystal surface-emitting lasers by using the transfer matrix method and coupled wave method to achieve a low-threshold operation. The extremely low-threshold gain is achieved by adopting an asymmetric cladding layer design to enhance both of the vertical optical confinement factors for the quantum wells and photonic crystal (PC). By modifying the composition of the AlGaAs layer to raise the refractive index in the p-type cladding, optical field distribution will obviously be shifted to the p side. Hence, it results in a significant coupling enhancement between the optical mode profile and the PC layer. The optimized value of the vertically optical confinement factor of the PC layer is 13.94%, and the corresponding threshold gain can be as low as 19.45 cm(-1). (C) 2013 Optical Society of America
Blue GaN-based surface-emitting lasers incorporating a sub-wavelength high contrast grating
(2013-01-01)
Wu, Tzeng-Tsong
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Wu, Shu-Hsien
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Chen, Hao-Wen
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Lu, Tien-Chang
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Wang, Shing-Chung
Blue GaN-based surface-emitting lasers incorporating a sub-wavelength high contrast grating were reported. The laser characteristics such as threshold energy, degree of polarization and divergence angle were measured to be 0.56 mJ/cm(2), 73% and 12 degrees. (C) 2013 Optical Society of America
Carrier localization degree of In(0.2)Ga(0.8)N/GaN multiple quantum wells grown on vicinal sapphire substrates
(2009-01-01)
Li, Zhen-Yu
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Lo, Ming-Hua
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Chiu, Ching-Hua
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Lin, Po-Chun
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Lu, Tien-Chang
In this work, we have grown In(0.2)Ga(0.8)N/GaN multiple quantum well (MQWs) epitaxial structure on vicinal sapphire substrates by low pressure metal-organic chemical vapor deposition and investigated the relationship between carrier localization degree and vicinal angles of sapphire substrates. The optical analysis confirmed that the In(0.2)Ga(0.8)N/GaN MQWs grown on 0.2 degrees-off sapphire substrate exhibited the smallest carrier localization degree and more ordered In(0.2)Ga(0.8)N/GaN MQW structure. In addition, mechanisms for carrier localization in In(0.2)Ga(0.8)N/GaN MQWs grown on vicinal substrate were discussed based on the results obtained from the power and temperature dependent photoluminescence measurements. The Raman spectrum showing the in-plane compressive stress of the GaN epitaxial structures grown on vicinal sapphire substrates revealed the relation between the dislocation density and the carrier localization degree in MQWs. From transmission electron microscopy images, the threading dislocation density (TDD) of In(0.2)Ga(0.8)N/GaN MQWs grown on 0.2 vicinal sapphire substrate at the bottom of n-GaN layer was about 9.4 X 10(8) cm(-2) and reduced to 3.0 X 10(8) cm(-2) at the top of n-GaN layer. We also obtained the TDD of 5.6 X 10(7) cm(-2) in the MQW region and only 1.0 X 10(7) cm(-2) in the p-GaN region. Based on the results mentioned above, 0.2 degrees-off substrate can offer In(0.2)Ga(0.8)N/GaN MQW blue light-emitting diode structures with benefits, such as high crystal quality, low defects, and small carrier localization degree. (C) 2009 American Institute of Physics. (DOI: 10.1063/1.3055264)
Carrier localization degree of In0.2Ga0.8N/GaN multiple quantum wells grown on vicinal sapphire substrates
(2009-01-01)
Li, Zhen-Yu
;
Lo, Ming-Hua
;
Chiu, Ching-Hua
;
Lin, Po-Chun
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Lu, Tien-Chang
In this work, we have grown In0.2Ga0.8N/GaN multiple quantum well (MQWs) epitaxial structure on vicinal sapphire substrates by low pressure metal-organic chemical vapor deposition and investigated the relationship between carrier localization degree and vicinal angles of sapphire substrates. The optical analysis confirmed that the In0.2Ga0.8N/GaN MQWs grown on 0.2 degrees-off sapphire substrate exhibited the smallest carrier localization degree and more ordered In0.2Ga0.8N/GaN MQW structure. In addition, mechanisms for carrier localization in In0.2Ga0.8N/GaN MQWs grown on vicinal substrate were discussed based on the results obtained from the power and temperature dependent photoluminescence measurements. The Raman spectrum showing the in-plane compressive stress of the GaN epitaxial structures grown on vicinal sapphire substrates revealed the relation between the dislocation density and the carrier localization degree in MQWs. From transmission electron microscopy images, the threading dislocation density (TDD) of In0.2Ga0.8N/GaN MQWs grown on 0.2 vicinal sapphire substrate at the bottom of n-GaN layer was about 9.4 X 10(8) cm(-2) and reduced to 3.0 X 10(8) cm(-2) at the top of n-GaN layer. We also obtained the TDD of 5.6 X 10(7) cm(-2) in the MQW region and only 1.0 X 10(7) cm(-2) in the p-GaN region. Based on the results mentioned above, 0.2 degrees-off substrate can offer In0.2Ga0.8N/GaN MQW blue light-emitting diode structures with benefits, such as high crystal quality, low defects, and small carrier localization degree. (C) 2009 American Institute of Physics. (DOI: 10.1063/1.3055264)
Characteristic of UV Plasmonic Nanolasers with Different Spacer Thickness
(2016)
Chou, Yu-Hsun
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Chou, Bo-Tsun
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Lin, Sheng-Di
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Lin, Tzy-Rong
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Lin, Chien-Chung
We report on plasmonic lasers with ZnO nanowire lying on single-crystalline silver film with different SiO2 thickness spacer. Spacer thickness were optimized to adjust the surface plasmon dispersion curve and resulting different group index.
Characteristics of a-Plane Green Light-Emitting Diode Grown on r-Plane Sapphire
(2009-08-15)
Ling, Shih-Chun
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Wang, Te-Chung
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Chen, Jun-Rong
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Liu, Po-Chun
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Ko, Tsung-Shine
In this work, we have successfully grown a-plane green light-emitting diodes (LEDs) on r-plane sapphire and investigated the device characteristics of a-plane green LEDs. The apparent emission polarization anisotropy was observed and the polarization degree was as high as 67.4%. In addition, the electroluminescence (EL) spectra first revealed a wavelength blue-shift with increasing drive current to 20 mA, which could be attributed to the band-filling effect, and then the EL peak become constant. The current-voltage curve showed the forward voltage of a-plane LED grown on r-plane sapphire substrate was 3.43 V and the differential series resistance was measured to be about 24 Omega as 20-mA injected current. Furthermore, the output power was 240 mu W at 100-mA drive current.