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Characterization and density control of GaN nanodots on Si (111) by droplet epitaxy using plasma-assisted molecular beam epitaxy
(2014-12-17)
Yu, Ing-Song
;
Chang, Chun-Pu
;
Yang, Chung-Pei
;
Lin, Chun-Ting
;
Ma, Yuan-Ron
In this report, self-organized GaN nanodots have been grown on Si (111) by droplet epitaxy method, and their density can be controlled from 1.1 x 10(10) to 1.1 x 10(11) cm(-2) by various growth parameters, such as substrate temperatures for Ga droplet formation, the pre-nitridation treatment of Si substrate, the nitridation duration for GaN crystallization, and in situ annealing after GaN formation. Based on the characterization of in situ RHEED, we can observe the surface condition of Si and the formation of GaN nanodots on Si. The surface nitridaiton treatment at 600 degrees C provides a-SiNx layer which makes higher density of GaN nanodots. Crystal GaN nanodots can be observed by the HRTEM. The surface composition of GaN nanodots can be analyzed by SPEM and mu-XPS with a synchrotron x-ray source. We can find GaN nanodots form by droplet epitaxy and then in situ annealing make higher-degree nitridation of GaN nanodots.
Wavelength-tunable InGaAs-capped quantum-dot infrared photodetectors for multi-color detection
(2011-05-01)
Lin, Wei-Hsun
;
Lin, Shih-Yen
;
Tseng, Chi-Che
;
Kung, Shu-Yen
;
Chao, Kuang-Ping
A two-terminal quantum-dot infrared photodetector (QDIP) with stacked 5-period InAs/GaAs and InGaAs-capped InAs/GaAs QD structures is investigated in this paper. The device has exhibited distinct responses at mid-wavelength and long-wavelength infrared regions under positive and negative biases, respectively. Also observed for the device are the equal normal absorption ratios under different voltage biases for the device under either MWIR or LWIR ranges. The device has revealed its potential in the application of voltage-tunable and multi-color detections. (C) 2010 Elsevier B.V. All rights reserved.
Analysis of InAsN quantum dots by transmission electron microscopy and photoluminescence
(2008-10-01)
Hsu, Chiung-Chih
;
Hsu, Ray-Quen
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Wu, Yue-Han
;
Chi, Tung-Wei
;
Chiang, Chen-Hao
Quantum dots (QDs) have great potential in optical fiber communication applications were widely recognized. The structure of molecular beam epitaxy (MBE) grew InAsN QDs were investigated by transmission electron microscopy (TEM) and measured their optical properties by photoluminescence (PL). TEM images show that the InAsN QDs are irregular or oval shaped. Some of the InAsN QDs are observed to have defects, such as dislocations at or near the surface in contrast to InAs QDs, which appear to be defect free. PL results for InAsN QDs showed a red-shifted emission peak. In addition, the InAsN emission peak is broader than InAs QDs, which supports the TEM observation that the size distribution of the InAsN QDs is more random than InAs QDs. The results show that the addition of nitrogen to InAs QDs leads to a decrease in the average size of the QDs, bring changes in the QD's shape, compositional distribution, and optical properties. (C) 2008 Published by Elsevier B.V.
The transition mechanisms of quantum-dot/quantum-well mixed-mode infrared photodetectors
(2009-11-01)
Lin, Shih-Yen
;
Chou, Shu-Ting
;
Lin, Wei-Hsun
;
光電工程學系
;
Department of Photonics
The transition mechanisms of a 10-period quantum-dot (QD)/quantum-well (QW) mixed-mode infrared photodetector is investigated in this paper. Both mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) responses are observed for the device. The lower normal incident absorption of the LWIR peak suggests that the QW intra-band transition is responsible for the response while the QD intra-band transition for the MWIR response. Due to the coexistence of MWIR and LWIR responses, the MWIR response should be resulted from one-photon transition while the LWIR response from the two-photon transition. To explain the transition mechanisms of the MMIP device, a model is proposed in this paper. The increases of both MWIR and LWIR responses with increasing measurement temperatures observed for the device are attributed to the increase of electrons in the QW ground state/wetting layer state resulted from the increase of one-photon absorption process with increasing temperatures. (C) 2009 Elsevier B.V. All rights reserved.
High-quality Quantum-Dot-Based Full-Color Display Technology by Pulsed Spray Method
(2013)
Chen, Kuo-Ju
;
Chen, Hsin-Chu
;
Tsai, Kai-An
;
Lin, Chien-Chung
;
Tsai, Hsin-Han
We fabricated the colloidal quantum-dot light-emitting diodes (QDLEDs) with the HfO2/SiO2-distributed Bragg reflector (DBR) structure using a pulsed spray coating method. Moreover, pixelated RGB arrays, 2-in. wafer-scale white light emission, and an integrated small footprint white light device were demonstrated. The experimental results showed that the intensity of red, blue, and green (RGB) emissions exhibited considerable enhancement because of the high reflectivity in the UV region by the DBR structure, which subsequently increased the use in the UV optical pumping of RGB QDs. In this experiment, a pulsed spray coating method was crucial in providing uniform RGB layers, and the polydimethylsiloxane (PDMS) film was used as the interface layer between each RGB color to avoid cross-contamination and self-assembly of QDs. Furthermore, the chromaticity coordinates of QDLEDs with the DBR structure remained constant under various pumping powers in the large area sample, whereas a larger shift toward high color temperatures was observed in the integrated device. The resulting color gamut of the proposed QDLEDs covered an area 1.2 times larger than that of the NTSC standard, which is favorable for the next generation of high-quality display technology.
Improving efficiency of InGaN/GaN multiple quantum well solar cells using CdS quantum dots and distributed Bragg reflectors
(2013-10-01)
Tsai, Yu-Lin
;
Lin, Chien-Chung
;
Han, Hau-Vei
;
Chang, Chun-Kai
;
Chen, Hsin-Chu
This work demonstrates hybrid InGaN/GaN multiple quantum well (MQW) solar cells with enhanced power conversion efficiency using colloidal CdS quantum dots (QDs) and back-side distributed Bragg reflectors (DBRs). CdS QDs can absorb ultraviolet (UV) photons, which are strongly absorbed by indium tin oxide (ITO), and they emit photons with a longer wavelength. This process improves the collection of photon-generated carriers and is known as the luminescence down-shifting (LDS). Accordingly, CdS QDs can compensate for the poor utilization of UV photons in an ITO layer, enhancing the external quantum efficiency (EQE) in the UV range. The DBRs on the back of the solar cells can reflect photons of longer wavelengths back into the absorber layer, increasing the EQE (380-440 nm). The combination of CdS QDs and DBRs results in broadband EQE enhancement, and yields an overall power conversion efficiency that is 20.7% better than that of a reference device without CdS QDs and DBRs. (C) 2013 Elsevier B.V. All rights reserved.
Rapid and sensitive detection of cancer cells by coupling with quantum dots and immunomagnetic separation at low concentrations
(2011-06-15)
Hsieh, Yi-Heui
;
Lai, Lee-Jene
;
Liu, Shih-Jen
;
Liang, Keng S.
;
電子物理學系
This work presents a rapid and sensitive method for detecting cancer cells at low concentration. In this method, two biomarkers of T-help cancer cells are detected simultaneously. One biomarker is conjugated with magnetic beads to separate T-help cell from the mixed cells and the other biomarker, associated with quantum dots, is used to detect fluorescence. The specific T-help cells can be quantified using the relationship between the QD fluorescence intensity and the cell frequency following magnetic separation. The intensity of fluorescence increases linearly with the frequency of T-help cells from 10(-7) to 10(-3), and neither B cells nor red blood cells interfere with the detection of T-help cells. Moreover, the total detection time is under 15 min, even though the frequency of specific T-help cells is as low as 5 x 10(-7). The numerous advantages of detecting specific cells at low concentration using the presented method include ease of preparation, low cost, fast detection, and high sensitivity. (C) 2011 Elsevier B.V. All rights reserved.
Infrared proximity sensor using organic light-emitting diode with quantum dots converter
(2012-11-01)
Chen, En-Chen
;
Yeh, Han-Cheng
;
Chao, Yu-Chiang
;
Meng, Hsin-Fei
;
Zan, Hsiao-Wen
An efficient visible-to-infrared conversion film is made by blending CdTe quantum dots (CdTe QDs) of 12 nm diameter in a polyvinylpyrrolidone 360 (PVP 360) polymer matrix cast by water solution. The solid-state photoluminescence quantum efficiency exceeds 10% with emission peak at 810 nm. Strong 810 emission is obtained by combining the quantum dot film and a green polyfluorene light-emitting diode. Color filter is used to remove residual light below 780 nm to make it entirely invisible. Infrared photo-detector is made by blending poly[5-(5-(2,5-bis(decyloxy)-4-methylphenyl)thiophen-2-yl)-2,3-bis(4-(2-ethylhexyloxy)phenyl)-7-(5-methylthiophen-2-yl)thieno[3,4-b]pyrazine] (PBDOTTP) with band-gap 1.2 eV and (6,6)-phenyl-C61-butyric acid methyl ester (PCBM). The pixel contains one PD surrounded by four PLED on its four sides. The active areas of the five devices are all I cm by 1 cm and they are on the same plane. Infrared proximity sensor with photo-current over 300 nA at 10 cm object distance is achieved by detecting the reflected infrared signal. (C) 2012 Elsevier B.V. All rights reserved.
Unusual Diamagnetism in Semiconductor Nano-Objects
(2010)
Thu, L. M.
;
Voskoboynikov, O.
;
交大名義發表
;
National Chiao Tung University
We theoretically consider the diamagnetic response of an InAs/GaAs asymmetrical nano-ring and asymmetrical quantum dot molecule when external magnetic field is applied in the system's growth directions. We use the effective one-electronic-band Hamiltonian (energy-position-dependent electron effective mass and g-factor approximation) with smooth full three-dimensional confinement potentials mapping actual strain and material content in those nano-objects. This approach allows us to simulate and study physical properties of semiconductor nano-objects within a wide range of change in geometry and parameters. Although the geometries of the systems investigated are very different, we found for both systems a similar magnetic response. At low temperature the single electron differential magnetic susceptibility has a positive peak and with temperature increasing the peak remain Lorenzt-like shaped and gradually disappear.
Enhancement of power conversion efficiency in GaAs solar cells with dual-layer quantum dots using flexible PDMS film
(2012-09-01)
Chen, Hsin-Chu
;
Lin, Chien-Chung
;
Han, Hau-Vei
;
Chen, Kuo-Ju
;
Tsai, Yu-Lin
"This study demonstrates the high performance of GaAs solar cells with dual-layer CdS quantum dots (QDs) carried by flexible polydimethylsiloxane (PDMS) film. Several parameters were enhanced, including the short circuit current, fill factor, and power conversion efficiency, which were measured under white light illumination similar to the solar spectrum. The flexible PDMS film was fabricated using the spin-coating technique, and was then used to embed dual-layer CdS QDs. Different concentrations of QDs were applied in this design to test the optimal combination. The proposed scheme enhances power conversion efficiency by 22%, compared to a GaAs solar cell without CdS QDs. The photon down-conversion capability in the ultraviolet (UV) range and additional antireflection capability in the longer visible-IR range were verified through the external quantum efficiency. (C) 2012 Elsevier B.V. All rights reserved."

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