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Now showing 1 - 10 of 163

Light emission characteristics of nonpolar a-plane GaN-based photonic crystal defect cavities
(2015-01-01)
Kao, Tsung Sheng
;
Wu, Tzeng-Tsong
;
Tsao, Che-Wei
;
Lin, Jyun-Hao
;
Lin, Da-Wei
In this paper, nonpolar a-plane GaN-based photonic crystals (PCs) with different defect cavities have been demonstrated. By using a micro-photoluminescence (mu-PL) system operated at 77 K, the dominant resonant modes of the GaN-based PC defect cavities show high quality factor (Q) values in the light emission performance which can be up to 4.3x10(3). Moreover, the degree of polarization (DOP) of the light emission from the nonpolar GaN-based PC defect cavities was measured to achieve around 64 % along the m crystalline direction.
Fabrication of SiC Membrane HCG Blue Reflector Using Nanoimprint Lithography
(2015-01-01)
Lai, Ying-Yu
;
Matsutani, Akihiro
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Lu, Tien-Chang
;
Wang, Shing-Chung
;
Koyama, Fumio
We designed and fabricated a suspended SiC-based membrane high contrast grating (HCG) reflectors. The rigorous coupled-wave analysis (RCWA) was employed to verify the structural parameters including grating periods, grating height, filling factors and air-gap height. From the optimized simulation results, the designed SiC-based membrane HCG has a wide reflection stopband (reflectivity (R) > 90%) of 135 nm for the TE polarization, which centered at 480 nm. The suspended SiC-based membrane HCG reflectors were fabricated by nanoimprint lithography and two-step etching technique. This achievement should have an impact on numerous III-N based photonic devices operating in the blue wavelength or even ultraviolet region.
Self-assembled Ni nanodot on SiO2 film-a novel reactive ion etching mask for Si nanopillar formation on Si substrate
(2006-01-01)
Lin, Huang-Shen
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Kao, Chih-Chiang
;
Kuo, Hao-Chung
;
Wang, Shing-Chung
;
Lin, Gong-Ru
By rapid thermal annealing the Ni film evaporated on thin SiO2 layer covered Si substrate, we have successfully demonstrated the self-aggregation of two-dimensional randomized Ni nano-dots on Si wafer. The thin oxide layer prevents the formation of NiSi2 compounds and facilitates the self-assembly of Ni nanodots from retaining the thermal power on SiO2 layer. This greatly shrinks the annealing time required for metallic nanodot formation from > 10 min to < 30 sec. With the advantage of the self-assemble Ni/SiO2 nano-dots based nano-mask, a large-area Si nano-pillar array with rod size of < 50 nm can be formatted on Si substrate through the induced coupled plasma reactive ion etching (ICPRIE) procedure. After removing Ni dots and the SiO2 film on the Si substrate, both the visible and near infrared photoluminescence from the Si nano-pillar sample were observed and analyzed.
Crossover from polariton lasing to exciton lasing in a strongly coupled ZnO microcavity
(2016-02-03)
Lai, Ying-Yu
;
Chou, Yu-Hsun
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Lan, Yu-Pin
;
Lu, Tien-Chang
;
Wang, Shing-Chung
Unlike conventional photon lasing, in which the threshold is limited by the population inversion of the electron-hole plasma, the exciton lasing generated by exciton-exciton scattering and the polariton lasing generated by dynamical condensates have received considerable attention in recent years because of the sub-Mott density and low-threshold operation. This paper presents a novel approach to generate both exciton and polariton lasing in a strongly coupled microcavity (MC) and determine the critical driving requirements for simultaneously triggering these two lasing operation in temperature <140 K and large negative polariton-exciton offset (<-133 meV) conditions. In addition, the corresponding lasing behaviors, such as threshold energy, linewidth, phase diagram, and angular dispersion are verified. The results afford a basis from which to understand the complicated lasing mechanisms in strongly coupled MCs and verify a new method with which to trigger dual laser emission based on exciton and polariton.
Numerical analysis on current and optical confinement of III-nitride vertical-cavity surface-emitting lasers
(2014-04-21)
Lai, Ying-Yu
;
Huang, Shen-Che
;
Ho, Tsung-Lin
;
Lu, Tien-Chang
;
Wang, Shing-Chung
We report on the numerical analysis of the electrical and optical properties of current-injected III-nitride based vertical-cavity surface-emitting lasers (VCSELs) with three types of current confinement schemes: the conventional planar-indium tin oxide (ITO) type, the AlN-buried type without ITO, and the hybrid type. The proposed hybrid structure, which combines an ITO layer and an intracavity AlN aperture, exhibits not only uniform current distribution but also enhanced lateral optical confinement. Thus, the hybrid type design shows remarkably better performance including lower threshold current and series resistance compared with the planar-ITO type and the AlN-buried type. Furthermore, the multi-transverse mode lasing behavior induced by strong index guiding of the AlN aperture is suppressed to single transverse mode operation by reducing the aperture size. Such design provides a powerful solution for the high performance III-N based VCSELs and is also viable by using current state of the art processing techniques. (C) 2014 Optical Society of America
ZnO-Based Microcavities Sculpted by Focus Ion Beam Milling
(2016-06-30)
Chang, Tsu-Chi
;
Hong, Kuo-Bin
;
Lai, Ying-Yu
;
Chou, Yu-Hsun
;
Wang, Shing-Chung
We reported an easy fabrication method to realize ZnO-based microcavities with various cavity shapes by focused ion beam (FIB) milling. The optical characteristics of different shaped microcavities have been systematically carried out and analyzed. Through comprehensive studies of cathodoluminescence and photoluminescence spectra, the whispering gallery mode (WGM) was observed in different shaped microcavities. Up further increasing excitation, the lasing action was dominated by these WGMs and matched very well to the simulated results. Our experiment shows that ZnO microcavities with different shapes can be made with high quality by FIB milling for specific applications of microlight sources and optical devices.
Electrically Pumped III-N Microcavity Light Emitters Incorporating an Oxide Confinement Aperture
(2017-01-05)
Lai, Ying-Yu
;
Chang, Tsu-Chi
;
Li, Ya-Chen
;
Lu, Tien-Chang
;
Wang, Shing-Chung
In this work, we report on electrically pumped III-N microcavity (MC) light emitters incorporating oxide confinement apertures. The utilized SiO2 aperture can provide a planar ITO design with a higher index contrast (similar to 1) over other previously reported approaches. The fabricated MC light emitter with a 15-mu m-aperture shows a turn-on voltage of 3.3 V, which is comparable to conventional light emitting diodes (LEDs), showing a good electrical property of the proposed structure. A uniform light output profile within the emission aperture suggesting the good capability of current spreading and current confinement of ITO and SiO2 aperture, respectively. Although the quality factor (Q) of fabricated MC is not high enough to achieve lasing action (similar to 500), a superlinear emission can still be reached under a high current injection density (2.83 kA/cm(2)) at 77 K through the exciton-exciton scattering, indicating the high potential of this structure for realizing excitonic vertical-cavity surface-emitting laser (VCSEL) action or even polariton laser after fabrication optimization.
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
High Efficiency GaN-based Light Emitting Diodes with Embedded Air Voids/SiO2 Nanomasks
(2012-01-01)
Chiu, Ching-Hsueh
;
Lin, Chien-Chung
;
Han, Hau-Vei
;
Lin, Da-Wei
;
Chen, Yan-Hao
We fabricated high efficiency LEDs with embedded micro-scale air voids and SiO2 nanomask exhibit smaller reverse-bias current and great enhancement of the light output (65% at 20mA) compared with the conventional LEDs.
Enhancing the Emission Efficiency of In0.2Ga0.8N/GaN MQW Blue LED by Using Appropriately Misoriented Sapphire Substrates
(2009-01-01)
Li, Zhen-Yu
;
Uen, Wu-Yih
;
Lo, Ming-Hua
;
Chiu, Ching-Hua
;
Lin, Po-Chun
In this paper, we report the fabrication of an In0.2Ga0.8N/GaN multiple-quantum-well (MQW) structure on vicinal sapphire substrates with a very small offset angle of 0-1 degrees by low-pressure metallorganic chemical vapor deposition. Our study demonstrates that the quality of the In0.2Ga0.8N/GaN MQW structure is very sensitive to the offset angle of the vicinal substrate. High-resolution X-ray diffraction analyses demonstrated high-order satellite peaks and clear fringes between them for all MQW structures fabricated, from which the interface roughness (IRN) was estimated. The IRN of the In0.2Ga0.8N/GaN MQW structure fabricated on 0.2 degrees off sapphire substrate was determined as 1.36% of the quantum well layer period. Besides, reciprocal lattice mapping was employed to examine the strain status of the MQW. The lattice relaxation of the same specimen mentioned above was estimated to be 7.4x10(-5). It is therefore manifested that an In0.2Ga0.8N/GaN MQW structure with abrupt interfaces and good layer periodicity was grown. From it, a shortest radiative lifetime of 14.2 ns and a lowest fluctuation of 5.6 meV in the emission energy of micro-photoluminescence mapping were achieved. In addition, superior material qualities of the whole film fabricated on 0.2 degrees off substrate were recognized by cross-sectional transmission electron microscopy. Based on the results mentioned above, a high-quality In0.2Ga0.8N/GaN MQW blue light, emitting diode (LED) has been fabricated on 0.2 degrees off substrate, which demonstrated a strong room-temperature electroluminescence emission at the wavelength of 465 nm and with the full width at half maximum of only 19 nm. The same device also showed an output power of 13.4 mW and an external quantum efficiency of 19.2%. Both these characteristics are improved drastically compared with the devices fabricated on the substrates with other offset angles. Conclusively, the use of an appropriately misoriented sapphire substrate is suggested to be effective for elevating the emission efficiency of In0.2Ga0.8N/GaN MQW blue LED fabricated thereon.

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