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Two-dimensional designed fabrication of subwavelength grating HCG mirror on Silicon-on-insulator
(2016-01-01)
Huang, Shen-Che
;
Hong, Kuo-Bin
;
Lu, Tien-Chang
;
He, Sailing
;
光電工程學系
We designed and fabricated a two dimensional high contrast subwavelength grating (HCG) mirrors. The computer-aided software was employed to verify the structural parameters including grating periods and filling factors. From the optimized simulation results, the designed HCG structure has a wide reflection stopband (reflectivity (R) >90%) of over 200 nm, which centered at telecommunication wavelength. The optimized HCG mirrors were fabricated by electron-beam lithography and inductively coupled plasma process technique. The experimental result was almost consistent with calculated data. This achievement should have an impact on numerous photonic devices helpful attribution to the integrated HCG VCSELs in the future.
Study of efficiency droop in InGaN/GaN light emitting diodes with V-shape pits
(2015-01-01)
Chang, Chiao-Yun
;
Li, Heng
;
Lu, Tien-Chang
;
光電工程學系
;
光電工程研究所
We invesstagated the relationship between the emission efficiency of InGaN/GaN multiple quantum wells (MQWs) and the V-shape pits (V-pits) forming along the threading dislocation (TD). The thinner InGaN/GaN MQWs on the side walls around V-pits would create higher local energy barriers, which can resist the carriers trapped into the non-radiative recombination centres within TDs. By inserting different InGaN/GaN superlattice (SLS) layers below the MQWs, sizes of V-pits could be properly controlled. It was found that the V-pit size on InGaN MQWs increased with increasing SLS layers, which could decrease energy barriers. On the contrary, the shorter distance between the TD center and V-pit boundary would increase the carrier capturing capability of TDs in smaller V-pits. By properly controlling the V-shape defect formation, the best internal quantum efficiency of about 70% f was found in the MQWs with underlying 15 periods SLS layers.
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
;
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.
Significant Improvement of GaN Crystal Quality with Ex-situ Sputtered AlN Nucleation Layers
(2016-01-01)
Chen, Shuo-Wei
;
Yang, Young
;
Wen, Wei-Chih
;
Li, Heng
;
Lu, Tien-Chang
Ex-situ sputtered AlN nucleation layer has been demonstrated effective to significantly improve crystal quality and electrical properties of GaN epitaxy layers for GaN based Light-emitting diodes (LEDs). In this report, we have successfully reduced X-ray (102) FWHM from 240 to 110 arcsec, and (002) FWHM from 230 to 101 arcsec. In addition, reverse-bias voltage (Vr) increased around 20% with the sputtered AlN nucleation layer. Furthermore, output power of LEDs grown on sputtered AlN nucleation layer can be improved around 4.0% compared with LEDs which is with conventional GaN nucleation layer on pattern sapphire substrate (PSS).
3D structural construction of GaN-based light emitting diode by confocal micro-Raman spectroscopy
(2016-01-01)
Li, Heng
;
Chang, Chiao-Yun
;
Cheng, Hui-Yu
;
Chen, Wei-Liang
;
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.
Single-crystalline aluminum film for ultraviolet plasmonic nanolasers
(2016-01-27)
Chou, Bo-Tsun
;
Chou, Yu-Hsun
;
Wu, Yen-Mo
;
Chung, Yi-Cheng
;
Hsueh, Wei-Jen
Significant advances have been made in the development of plasmonic devices in the past decade. Plasmonic nanolasers, which display interesting properties, have come to play an important role in biomedicine, chemical sensors, information technology, and optical integrated circuits. However, nanoscale plasmonic devices, particularly those operating in the ultraviolet regime, are extremely sensitive to the metal and interface quality. Thus, these factors have a significant bearing on the development of ultraviolet plasmonic devices. Here, by addressing these material-related issues, we demonstrate a low-threshold, high-characteristic-temperature metal-oxide-semiconductor ZnO nanolaser that operates at room temperature. The template for the ZnO nanowires consists of a flat single-crystalline Al film grown by molecular beam epitaxy and an ultrasmooth Al2O3 spacer layer synthesized by atomic layer deposition. By effectively reducing the surface plasmon scattering and metal intrinsic absorption losses, the high-quality metal film and the sharp interfaces formed between the layers boost the device performance. This work should pave the way for the use of ultraviolet plasmonic nanolasers and related devices in a wider range of applications.
Crossover from polariton lasing to exciton lasing in a strongly coupled ZnO microcavity
(2016-02-03)
Lai, Ying-Yu
;
Chou, Yu-Hsun
;
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.
Exciton-polariton Josephson junctions at finite temperatures
(2017-08-25)
Lebedev, M. E.
;
Dolinina, D. A.
;
Hong, Kuo-Bin
;
Lu, Tien-Chang
;
Kavokin, A. V.
We consider finite temperature effects in a non-standard Bose-Hubbard model for an exciton-polariton Josephson junction (JJ) that is characterised by complicated potential energy landscapes (PEL) consisting of sets of barriers and wells. We show that the transition between thermal activation (classical) and tunneling (quantum) regimes exhibits universal features of the first and second order phase transition (PT) depending on the PEL for two polariton condensates that might be described as transition from the thermal to the quantum annealing regime. In the presence of dissipation the relative phase of two condensates exhibits non-equilibrium PT from the quantum regime characterized by efficient tunneling of polaritons to the regime of permanent Josephson or Rabi oscillations, where the tunneling is suppressed, respectively. This analysis paves the way for the application of coupled polariton condensates for the realisation of a quantum annealing algorithm in presently experimentally accessible semiconductor microcavities possessing high (105 and more) Q-factors.
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

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