Browsing by Author "Lu, Tien Chang"

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A novel randomly textured phosphor structure for highly efficient white light-emitting diodes
(2012-03-16)
Chen, Hsin Chu
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Chen, Kuo Ju
;
Wang, Chao Hsun
;
Lin, Chien Chung
;
Yeh, Chia Chi
We have successfully demonstrated the enhanced luminous flux and lumen efficiency in white light-emitting diodes by the randomly textured phosphor structure. The textured phosphor structure was fabricated by a simple imprinting technique, which does not need an expensive dry-etching machine or a complex patterned definition. The textured phosphor structure increases luminous flux by 5.4% and 2.5% at a driving current of 120 mA, compared with the flat phosphor and half-spherical lens structures, respectively. The increment was due to the scattering of textured surface and also the phosphor particles, leading to the enhancement of utilization efficiency of blue light. Furthermore, the textured phosphor structure has a larger view angle at the full width at half maximum (87A degrees) than the reference LEDs.
Effects of Inhomogeneous Gain and Loss on Nitride-Based Vertical-Cavity Surface Emitting Lasers
(2009-04-01)
Chen, Shih Wei
;
Lo, Ming Hua
;
Kao, Tsung Ting
;
Kao, Chih Chiang
;
Chu, Jung Tang
Nitride-based vertical cavity surface emitting lasers (VCSEL) with hybrid mirror has been investigated. We further measured the as-grown samples (without top dielectric distributed Bragg reflector) by p-photoluminescence, scanning near-field optical microscopy, and cathodoluminescence (CL). By different excitation power density, the experimental results indicated that the VCSEL devices have different lasing modes and spot sizes, represented inhomogeneous gain and loss distribution in the whole structure. The non-uniform emission intensity distribution including several bright spots of about 1 to 2 pm was observed for both VCSEL devices and as-grown samples, which was obtained from CL measurement, due to the effect of indium clusters and non-uniform micro-cavity resonant in InGaN multi-quantum wells (MQWs). The results show the significant influence on commercial applications such as light emitting diodes, lasers devices and so on. (C) 2009 The Japan Society of Applied Physics
GaSb-based Mid Infrared Photonic Crystal Surface Emitting Laser
(2015)
Pan, Chien Hung
;
Lin, Chien Hung
;
Chang, Tien Yuan
;
Lu, Tien Chang
;
Lee, Chien Ping
We demonstrate an optically pumped GaSb-based mid-Infrared photonic crystal surface emitting laser (PCSEL) at 2.3 mu m with line width of 0.3nm. The PCSEL was operated with temperature up to 350K, showing a shift rate of 0.21 nm/K.
GaSb-based mid infrared photonic crystal surface emitting lasers
(2015-05-04)
Pan, Chien Hung
;
Lin, Chien Hung
;
Chang, Ting Yuan
;
Lu, Tien Chang
;
Lee, Chien Ping
We demonstrated for the first time above room temperature (RT) GaSb-based mid-infrared photonic crystal surface emitting lasers (PCSELs). The lasers, under optical pumping, emitted at lambda(lasing) similar to 2.3 mu m, had a temperature insensitive line width of 0.3nm, and a threshold power density (P-th) similar to 0.3KW/cm(2) at RT. Type-I InGaAsSb quantum wells were used as the active region, and the photonic crystal, a square lattice, was fabricated on the surface to provide optical feedback for laser operation and light coupling for surface emission. The PCSELs were operated at temperatures up to 350K with a small wavelength shift rate of 0.21 nm/K. The PCSELs with different air hole depth were studied. The effect of the etched depth on the laser performance was also investigated using numerical simulation based on the coupled-wave theory. Both the laser wavelength and the threshold power decrease as the depth of the PC becomes larger. The calculated results agree well with the experimental findings. (C) 2015 Optical Society of America
Investigation of Composition-Dependent Optical Phonon Modes in Al(x)Ga(1-x)N Epitaxial Layers Grown on Sapphire Substrates
(2009)
Chen, Jun Rong
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Lu, Tien Chang
;
Kuo, Hao-Chung
;
Wang, Shing Chung
;
光電工程學系
We reported the systematical study of optical properties of hexagonal Al(x)Ga(1-x)N epitaxial films grown on c sapphire substrate using metal organic chemical vapor deposition By performing Fourier transform infrared spectroscopy measurements, the high-frequency dielectric constants and phonon frequencies can be obtained by theoretically fitting the experimental infrared reflectance spectra using a four phase layered model The high frequency dielectric constant of Al(x)Ga(1-x)N varies between 4 98 and 4 52 for epsilon(infinity) (perpendicular to) (polarization perpendicular to the optical axis) and between 4 95 and 4 50 for epsilon(infinity//) (polarization parallel to the optical axis) respectively when the aluminum composition changes from 0 15 to 024 Furthermore, from experimental Infrared reflectance spectra of Al(x)Ga(1-x)N films, a specific absorption dip at 785 cm(-1) was observed when the aluminum composition is larger than 0 24 The dip intensity increases and the dip frequency shifts from 785 to 812 cm-1 as aluminum composition increases from 0 24 to 0 58 According to the reciprocal space map of x-ray diffraction measurements, the emergence of this dip could be resulted from the effects of strain relaxation in AlGaN epitaxial layers due to the large lattice mismatch between GaN and AlGaN epitaxial film
Study of GaN-Based Photonic Crystal Surface-Emitting Lasers (PCSELs) With AlN/GaN Distributed Bragg Reflectors
(2009-05-01)
Chen, Shih Wei
;
Lu, Tien Chang
;
Kao, Tsung Ting
;
光電工程學系
;
Department of Photonics
GaN-based 2-D photonic crystal (PC) surface-emitting lasers (PCSELs) with AlN/GaN distributed Bragg reflectors are fabricated and investigated. A clear threshold characteristic under the optical pumping at room temperature is observed at about 2.7 mJ/cm(2) with PC lattice constant of 234 nm. Above the threshold, only one dominant peak appears at 401.8 nm with a linewidth of 0.16 nm. The laser emission covers whole circular 2-D PC patterns of 50 mu m in diameter with a small divergence angle. The lasing wavelength emitted from 2-D PC lasers with different lattice constants occurs at the calculated band edges, showing different polarization angles due to the light diffracted in specific directions, corresponding exactly to Gamma-, K-, and M-directions in the K space. The PCSEL also shows a spontaneous emission coupling factor beta of 5 x 10(-3) and a characteristic temperature of 148 K. Furthermore, the coupled-wave model in 2-D hexagonal lattice is applied to distinguish the discrepancy in threshold power and the corresponding coupling coefficient. The results show that the lasing actions within Gamma, K, and M modes have a substantial relation between the threshold energy density and the coupling coefficient.
Sub-wavelength GaN-based membrane high contrast grating reflectors
(2012-08-27)
Wu, Tzeng Tsong
;
Syu, Yu Cheng
;
Wu, Shu Hsien
;
Chen, Wei Ting
;
Lu, Tien Chang
The GaN-based membrane high contrast grating (HCG) reflectors have been fabricated and investigated. The structural parameters including grating periods, grating height, filling factors and air-gap height were calculated to realize high reflectivity spectra with broad bandwidth by the rigorous coupled-wave analysis and finite-difference time-domain method. Based on the optimized simulation results, the GaN-based membrane HCGs were fabricated by e-beam lithography and focused-ion beam process. The fabricated GaN-based membrane HCG reflectors revealed high reflectivity at 460 nm band with large stopband width of 60 nm in the TE polarization measured by using the micro-reflectivity spectrometer. The experimental results also showed a good agreement with simulated ones. We believe this study will be helpful for development of the GaN-based novel light emitting devices in the blue or UV region. (C) 2012 Optical Society of America
Suspended GaN-based band-edge type photonic crystal nanobeam cavities
(2014-02-10)
Wu, Tzeng Tsong
;
Chen, Hao Wen
;
Lan, Yu Pin
;
Lu, Tien Chang
;
Wang, Shing Chung
We demonstrated GaN-based photonic crystal (PC) nanobeam cavities by using the e-beam lithography and the suspended nanobeams were realized by focused-ion beam (FIB) milling. One resonant mode was clearly observed at 411.7 nm at 77K by optical pumping. The quality factor was measured to be to 7.4 x 10(2). Moreover, the degree of polarization value was measured to be 40%. The temperature-dependent characteristics were measured and discussed, which unambiguously demonstrated that the observed resonant peak originated from the band-edge mode of the one-dimensional PC nanobeam. (C) 2014 Optical Society of America
UVA light-emitting diode grown on Si substrate with enhanced electron and hole injections
(2017-11-01)
Zhang, Zi-Hui
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Chu, Chunshuang
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Chiu, Ching Hsueh
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Lu, Tien Chang
;
Li, Luping
In this work, III-nitride based similar to 370 nm UVA lightemitting diodes (LEDs) grown on Si substrates are demonstrated. We also reveal the impact of the AlN composition in the AlGaN quantum barrier on the carrier injection for the studied LEDs. We find that, by properly increasing the AlN composition, both the electron and hole concentrations in the multiple quantum wells (MQWs) are enhanced. We attribute the increased electron concentration to the better electron confinement within the MQW region when increasing the AlN composition for the AlGaN barrier. The improved hole concentration in the MQW region is ascribed to the reduced hole blocking effect by the p-type electron blocking layer (p-EBL). This is enabled by the reduced density of the polarization-induced positive charges at the AlGaN last quantum barrier (LB)/p-EBL interface, which correspondingly suppresses the hole depletion at the AlGaN LB/p-EBL interface and decreases the valence band barrier height for the p-EBL. As a result, the optical power is improved. (C) 2017 Optical Society of America