Browsing by Author "Lin, Wei-Hsun"

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Arbitrary waveform synthesis by multiple harmonics generation and phasing in aperiodic optical superlattices
(2009-08-31)
Lin, Wei-Hsun
;
Kung, A. H.
;
光電工程學系
;
Department of Photonics
The process of generating periodic optical waveforms includes the generation and phasing of several harmonics of a fundamental frequency. In this work, we show that simultaneous generation and phasing of the harmonics can be performed in a monolithic aperiodic optical superlattice (AOS). Stable periodic waveforms can thus be delivered to a predetermined location by simply sending a laser beam through a properly designed and fabricated AOS crystal. A detailed mathematical description for generating the domain pattern in such an AOS crystal is given and the process is numerically demonstrated. The waveform that is generated from a monolithic AOS is highly reproducible and phase stable. We also use propagation in air as an example to show how any predictable phase and amplitude modifications such as air dispersion that will alter the desired waveform can be pre-compensated in the design phase of the AOS crystal. (C) 2009 Optical Society of America
Broadband InGaAs-capped InAs/GaAs quantum-dot infrared photodetector with Bi-modal dot height distributions
(2012-08-01)
Lin, Wei-Hsun
;
Lin, Shih-Yen
;
光電工程學系
;
Department of Photonics
The influence of quantum-dot (QD) height distribution on the detection wavelengths of InGaAs-capped quantum-dot infrared photodetectors (QDIPs) is investigated. For devices with 2.8 and 2.0 mono-layer (ML) InAs coverage, 7.6 and 10.4 mu m detection wavelengths are observed. The results suggest that reduced dot height would result in a longer detection wavelength. By using 2.4 ML InAs QDs with bi-modal dot height distributions, a 6-12 mu m broadband QDIP is achieved with the combination of similar to 8 and similar to 10 mu m peak detection wavelengths contributed by the larger and smaller InAs QDs. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4745052]
Broadband Quantum-Dot Infrared Photodetector
(2010-07-01)
Lin, Wei-Hsun
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Tseng, Chi-Che
;
Chao, Kuang-Ping
;
Kung, Shu-Yen
;
Lin, Shih-Yen
In this letter, we report the five-period quantum-dot infrared photodetectors (QDIPs) with a bi-stacked quantum-dot (QD) structure for a wide and relatively flat detection response ranging from 4 to 11 m with high responsivities. The bi-stacked QD structure consists of a standard InAs QD and an InGaAs-capped InAs QD layer separated by a 50-nm GaAs barrier layer. The device exhibits a wide detection window in the range of 4-11 mu m with high responsivities, which suggests that similar responsivities can be obtained for the standard QD and the InGaAs-capped QD layers in the mid-wavelength (MWIR) and long-wavelength (LWIR) infrared ranges, respectively. The results are advantageous for the development of broadband QDIPs covering MWIR and LWIR ranges based on the stacked QD structures.
Compact microdisk cavity laser with type-II GaSb/GaAs quantum dots
(2011-01-31)
Hsu, K. S.
;
Chiu, T. T.
;
Lin, Wei-Hsun
;
Chen, K. L.
;
Shih, M. H.
Microdisk lasers with active region made of type-II GaSb/GaAs quantum dots on the GaAs substrate have been demonstrated. A microdisk cavity with diameter of 3.9 mu m was fabricated from a 225-nm-thick GaAs layer filled with GaSb quantum dots. Lasing at wavelengths near 1000 nm at 150 K was achieved for this microdisk. A high threshold characteristic temperature of 77 K was also observed. It is found that the lasing wavelength matches closely with the first-order whispering-gallery mode of the cavity as obtained from the finite-element method simulation. (c) 2011 American Institute of Physics. [doi: 10.1063/1.3543839]
Enhanced normal-incident absorption of quantum-dot infrared photodetectors with smaller quantum dots
(2008-07-01)
Tseng, Chi-Che
;
Chou, Shu-Ting
;
Chen, Yi-Hao
;
Chen, Cheng-Nan
;
Lin, Wei-Hsun
Ten-period InAs-GaAs quantum-dot (QD) infrared photodetectors grown under different In adatom supply procedures are investigated. Two In adatom supply procedures of In shutter 1) always opened and 2) periodically opened/closed are adopted in this letter. Larger QD sizes in both height and diameter and more uniform size distribution are observed for samples grown under an In shutter periodically opened/closed condition. The device with QDs grown under the In shutter always opened condition has revealed shorter detection wavelengths and enhanced normal incident absorption. The phenomenon shows that beside the increase of energy difference between confinement states, smaller QD sizes would also enhance the normal incident absorption predicted for the theoretically zero-dimensional QD structures.
Enhancement of operation temperature of InAs/GaAs quantum-dot infrared photodetectors with hydrogen-plasma treatment
(2009-09-01)
Lin, Wei-Hsun
;
Tseng, Chi-Che
;
Chao, Kuang-Ping
;
Lin, Shih-Yen
;
Wu, Meng-Chyi
Postprocess hydrogen treatment is performed over fabricated ten-period InAs/GaAs quantum-dot infrared photodetectors. While keeping similar spectral responses at the same applied voltage, a reduced dark current is observed for the H-plasma-treated device, which is attributed to the suppression of surface leakage-current induced by surface damage during device processing. The significant reduction in dark current also enhanced the operation temperature of the device up to 100 K. Also observed are the smoothed-out mesa edges after the H-plasma treatment, which results in trapezoidal mesa edges. In this case, a longer propagation length in the device of the reflected incident light at the mesa edge would enhance the normal-incident absorption ratio of the H-plasma-treated device. (C) 2009 American Vacuum Society. [DOI:10.1116/1.3196781]
Improved 1.3-mu m Electroluminescence of InGaAs-Capped Type-II GaSb/GaAs Quantum Rings at Room Temperature
(2013-01-01)
Lin, Wei-Hsun
;
Wang, Kai-Wei
;
Lin, Shih-Yen
;
Wu, Meng-Chyi
;
光電學院
Room-temperature 1.3-mu m electroluminescence is observed for the InGaAs-capped GaSb quantum rings (QRs). The increasing carrier density in the InGaAs-capped type-II GaSb QRs would induce a larger blue shift in the same laser pumping power span and enhance the luminescence intensity. The enhanced luminescence intensity, a larger blue shift of peak wavelength, and 1.3-mu m emission of the InGaAs-capped QR structure have revealed its potential application in multi-wavelength light-emitting devices in the near infrared range.
In-Plane Gate Transistors for Photodetector Applications
(2013-06-01)
Liao, Yu-An
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Lin, Wei-Hsun
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Chao, Yi-Kai
;
Chang, Wen-Hao
;
Chyi, Jen-Inn
In-plane gate transistors (IPGTs) with 20-mu m channel widths are fabricated on samples with n-(InGa)As sheet resistance embedded in undoped GaAs matrix. A trade-off between effective current modulation and high saturation drain current is obtained by optimizing the doping density of the sheet resistance. The mechanism responsible for the transistor behaviors of the devices is due to the channel electron depletion related to the population of mobile surface electrons under different gate biases. The photocurrent measurements demonstrate that the IPGT architecture is a feasible approach for the applications of photodetectors.
In-Plane Gate Transistors With a 40-mu m-Wide Channel Width
(2012-08-01)
Chung, Tung-Hsun
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Lin, Wei-Hsun
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Chao, Yi-Kai
;
Chang, Shu-Wei
;
Lin, Shih-Yen
An in-plane gate transistor with a GaAs/AlGaAs 2-D electron-gas channel about 40 mu m in width is investigated. The saturation region and the drain current modulation at different gate bias voltages are observed despite the wide channel. The surface-induced channel depletion is suggested as the main mechanism for the turn-off of the drain current at -10 V gate bias.
Influence of As on the Morphologies and Optical Characteristics of GaSb/GaAs Quantum Dots
(2011-03-01)
Tseng, Chi-Che
;
Mai, Shu-Cheng
;
Lin, Wei-Hsun
;
Wu, Shung-Yi
;
Yu, Bang-Ying
The influence of As atoms on the morphologies of GaSb quantum dots (QDs) is investigated. Without any special treatment, GaSb quantum rings (QRs) are observed in the embedded GaSb layer even when the uncapped layer reveals QD-like morphologies. With intentional As supply after the uncapped GaSb QD deposition, a QD to QR transition is observed. The phenomenon suggests that insufficient Sb atoms on the GaSb QDs would lead to the QD to QR transition as in the case of embedded GaSb layers. With extended Sb soaking time following GaSb deposition, QD structures could be well maintained for the embedded GaSb layers. A light-emitting diode operated at room temperature is fabricated based on the GaSb/GaAs QD structure. Identical peak positions in photoluminescence and electroluminescence (EL) spectra of the device show that type-II GaSb QDs are responsible for the observed EL.
InGaAs-Capped InAs-GaAs Quantum-Dot Infrared Photodetectors Operating in the Long-Wavelength Infrared Range
(2009-09-15)
Lin, Wei-Hsun
;
Tseng, Chi-Che
;
Chao, Kuang-Ping
;
Mai, Shu-Cheng
;
Lin, Shih-Yen
A ten-period InAs-GaAs quantum-dot infrared photodetector (QDIP) with 8-nm In(0.15)Ga(0.85) As capping layer grown after quantum-dot (QD) deposition is investigated. With reduced InAs QD coverage down to 2.0 mono-layers, responses at 10.4 and 8.4 mu m are observed for the device under positive and negative biases, respectively. The phenomenon is attributed to the large Stark effect resulted from the asymmetric band diagrams of the device under different voltage polarities. The demonstration of long-wavelength infrared detections with the simple structures of the InGaAs-capped QDIP is advantageous for the development of multicolor QDIP focal-plane arrays.
Lasing action and extraordinary reduction in long radiative lifetime of type-II GaSb/GaAs quantum dots using circular photonic crystal nanocavity
(2015-08-31)
Hsu, Kung-Shu
;
Hung, Wei-Chun
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Chang, Chih-Chi
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Lin, Wei-Hsun
;
Shih, Min-Hsiung
We demonstrated the lasing action and remarkable reduction in long radiative lifetimes of type-II GaSb/GaAs quantum dots using a circular photonic-crystal nano-cavity with high Purcell factors. The associated enhancement in carrier recombination was surprisingly high and could even surpass type-I counterparts in similar conditions. These phenomena reveal that the type-II sample exhibited extremely low nonradiative recombination so that weak radiative transitions were more dominant than expected. The results indicate that type-II nanostructures may be advantageous for applications which require controllable radiative transitions but low nonradiative depletions. (C) 2015 AIP Publishing LLC.
Long-wavelength electroluminescence of InGaAs-capped type-II GaSb/GaAs quantum-rings at room temperature
(2013-09-01)
Lin, Wei-Hsun
;
Wang, Kai-Wei
;
Lin, Shih-Yen
;
Wu, Meng-Chyi
;
光電學院
The room-temperature photoluminescence (PL) and electroluminescence (EL) exceeding 1.3 mu m are observed for InGaAs-capped GaSb quantum-ring (QR) structures. With increasing In composition, the emission wavelength would shift from 1.18 to 131 mu m. The InGaAs-capped GaSb QRs also exhibit a higher injection current and stronger EL intensity at the same applied voltage. With the observation of low-temperature PL spectra, the transition mechanisms of the standard and InGaAs-capped QRs are further investigated. (c) 2012 Elsevier B.V. All rights reserved.
Photonic Crystal Circular Nanobeam Cavity Laser with Type-II GaSb/GaAs Quantum Rings as Gain Material
(2020-03-16)
Lin, Hsiang-Ting
;
Hsu, Kung-Shu
;
Chang, Chih-Chi
;
Lin, Wei-Hsun
;
Lin, Shih-Yen
The optical emission from type-II semiconductor nanostructures is influenced by the long carrier lifetime and can exhibit remarkable thermal stability. In this study, utilizing a high quality photonic crystal circular nanobeam cavity with a high quality factor and a sub-micrometer mode volume, we demonstrated an ultra-compact semiconductor laser with type-II gallium antimonide/gallium arsenide quantum rings (GaSb/GaAs QRs) as the gain medium. The lasing mode localized around the defect region of the nanobeam had a small modal volume and significant coupling with the photons emitted by QRs. It leads the remarkable shortening of carrier lifetime observed from the time-resolved photoluminescence (TRPL) and a high Purcell factor. Furthermore, a high characteristic temperature of 114K was observed from the device. The lasing performances indicated the type-II QRs laser is suitable for applications of photonic integrated circuit and bio-detection applications.
Room-Temperature Electro-Luminescence of Type-II GaSb/GaAs Quantum Rings
(2012-07-15)
Lin, Wei-Hsun
;
Lin, Meng-Yu
;
Wu, Shung-Yi
;
Lin, Shih-Yen
;
光電工程學系
The influence of Sb/background As flux ratios on GaSb nano-structures is investigated in this letter. With decreasing Sb/background As flux ratios under high Sb irradiation during the post soaking procedure, ring formation, photoluminescence (PL) intensity enhancement, and PL peak red shift are observed. With further reduced Sb flux and Sb/background As ratios, the observed more intense PL intensities of the quantum-ring (QR) samples compared with quantum dots suggest that more electron-hole wave function overlapping is obtained. The observation of room-temperature electro-luminescence of a QR PIN diode has revealed the potential of the nano-structure in light-emitting device application.
Room-temperature operation type-II GaSb/GaAs quantum-dot infrared light-emitting diode
(2010-03-22)
Lin, Shih-Yen
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Tseng, Chi-Che
;
Lin, Wei-Hsun
;
Mai, Shu-Cheng
;
Wu, Shung-Yi
A GaSb/GaAs quantum-dot light-emitting diode (QD LED) with a single GaSb QD layer is investigated in this paper. The room-temperature photoluminescence peak blueshift with increasing excitation power densities suggests a type-II alignment of the GaSb/GaAs heterostructures. Significant electroluminescence (EL) is observed for the device under forward biases, which suggests that pronounced dipole transitions occur at the GaSb/GaAs interfaces. With increasing forward biases, the observed EL peak blueshift confirms that the origin of luminescence is from the type-II GaSb/GaAs QD structures. A model is established to explain the operation mechanisms of the type-II QD LED.
Temperature-dependent photoluminescence and carrier dynamics of standard and coupled type-II GaSb/GaAs quantum rings
(2013-09-01)
Lin, Wei-Hsun
;
Wang, Kai-Wei
;
Lin, Shih-Yen
;
Wu, Meng-Chyi
;
光電學院
Temperature-dependent photoluminescence (PL) and the corresponding carrier dynamics of standard and coupled type-II GaSb/GaAs quantum rings (QRs) are investigated in this article. Compared with standard QRs, the slower PL intensity decay of coupled QRs with increasing temperature is attributed to the depression of thermal quenching. More intense PL intensity is also observed for the coupled-QR sample at room temperature. With further reducing the GaAs spacer layer thickness to 2 nm, near two-times PL enhancement is observed. The results indicate that with the enhanced luminescence intensity of coupled-QR structure, type-II nano-structures may be utilized for light-emitting device applications. (c) 2013 Elsevier B.V. All rights reserved.
The formation mechanisms and optical characteristics of GaSb quantum rings
(2013-08-07)
Lin, Wei-Hsun
;
Wang, Kai-Wei
;
Liao, Yu-An
;
Pao, Chun-Wei
;
Lin, Shih-Yen
The growth mechanisms and optical characteristics of GaSb quantum rings (QRs) are investigated. Although As-for-Sb exchange is the mechanism responsible for the dot-to-ring transition, significant height difference between GaSb quantum dots (QDs) and QRs in a dot/ring mixture sample suggests that the dot-to-ring transition is not a spontaneous procedure. Instead, it is a rapid transition procedure as long as it initiates. A model is established to explain this phenomenon. Larger ring inner diameters and heights of the sample with longer post Sb soaking time suggest that As-for-Sb exchange takes places in both vertical and lateral directions. The decreasing ring densities, enlarged ring inner/outer diameters and eventually flat GaSb surfaces observed with increasing growth temperatures are resulted from enhanced adatom migration and As-for-Sb exchange with increasing growth temperatures. (C) 2013 AIP Publishing LLC.
The influence of background As on GaSb/GaAs quantum dots and its application in infrared photodetectors
(2012)
Lin, Wei-Hsun
;
Tseng, Chi-Che
;
Wu, Shung-Yi
;
Wu, Meng-Hsun
;
Lin, Shih-Yen
In this paper, GaSb nanostructures prepared under different Sb/background As ratios are investigated. With decreasing Sb/background As ratios, the morphologies of GaSb nanostructure changing from quantum dots (QDs) to quantum rings (QRs) are observed. The higher optical recombination probabilities of GaSb QRs are attributed to enhanced electron-hole wave function overlapping and more surrounding electrons around the GaSb QR core shell. With well-control Sb/background As ratios, the high-temperature operation GaSb quantum-dot infrared photodetector (QDIP) with simple stacked structure has been demonstrated. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
The influence of In composition on InGaAs-capped InAs/GaAs quantum-dot infrared photodetectors
(2009-09-01)
Lin, Wei-Hsun
;
Chao, Kuang-Ping
;
Tseng, Chi-Che
;
Mai, Shu-Cheng
;
Lin, Shih-Yen
The influence of an additional InGaAs-capped layer on the performance of InAs/GaAs quantum-dot infrared photodetectors (QDIPs) is investigated. For the device with a 15% InGaAs-capped layer, a significant response at 7.9 mu m is observed for the QDIP device. The results suggest that with the additional InGaAs-capped layer, the detection wavelengths of the InAs/GaAs QDIPs could be shifted to a longer-wavelength infrared range. A further increase in the In composition will not help to obtain an even longer-wavelength detection, which is attributed to the cancellation of a lower InGaAs state, and InAs-QD bandgap shrinkage resulted from the relaxed compressive strains of the InGaAs layer with a higher In composition.