Browsing by Author "Wang, Shing Chung"

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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
Investigation of Composition-Dependent Optical Phonon Modes in Al(x)Ga(1-x)N Epitaxial Layers Grown on Sapphire Substrates
(2009)
Chen, Jun Rong
;
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
Lasing at exciton transition in optically pumped gallium nitride nanopillars
(2011-09-12)
Lo, Ming-Hua
;
Cheng, Yuh-Jen
;
Liu, Mei-Chun
;
Kuo, Hao-Chung
;
Wang, Shing Chung
We report the observation of room temperature lasing action in optically pumped GaN nanopillars. The nanopillars were fabricated by patterned etching and crystalline regrowth from a GaN substrate. When nanopillars were optically excited, a narrow emission peak emerged from the broad spontaneous emission background. The increasing rate is nine times faster than that of the spontaneous emission background, showing the onset of lasing action. The lasing occurs right at the center of spontaneous emission rather than the often reported redshifted wavelength. A spectroscopic ellipsometry analysis indicates that the gain of lasing action is provided by exciton transition. (C) 2011 Optical Society of America
Metal organic chemical vapor deposition growth of GaN-based light emitting diodes with naturally formed nano pyramids
(2008-04-01)
Chiu, Ching-Hua
;
Lee, Chia-En
;
Lo, Ming-Hua
;
Huang, Hung-Wen
;
Lu, Tien-Chang
GaN-based light-emitting diodes (LEDs) with naturally formed nano pyramids roughened surfaces grown by metal organic chemical vapor deposition (MOCVD) were demonstrated. In this study, Mg-treatment, a growth-.interruption step and a surface treatment using biscyclopentadienyl magnesium (CP(2)Mg), was performed to form the nano pyramids on the surface of a p-type cladding layer, and then a p-type contact layer was grown on the p-type cladding layer, so as to create a p-type contact layer with a rough surface. Assisted by the nano pyramids surface roughening process, the light output power of the LEDs reached 11.3 and 9.7 mW with 10 and 5 min Mg-treatment at a driving current of 20 mA. The light outputs were increased by 48 and 27%, respectively, compared with the results from the LED without Mg-treatment.
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