Browsing by Author "Lo, Ming-Cheng"

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Atomic-scale epitaxial aluminum film on GaAs substrate
(2017-07-01)
Fan, Yen-Ting
;
Lo, Ming-Cheng
;
Wu, Chu-Chun
;
Chen, Peng-Yu
;
Wu, Jenq-Shinn
Atomic-scale metal films exhibit intriguing size-dependent film stability, electrical conductivity, superconductivity, and chemical reactivity. With advancing methods for preparing ultra-thin and atomically smooth metal films, clear evidences of the quantum size effect have been experimentally collected in the past two decades. However, with the problems of small-area fabrication, film oxidation in air, and highly-sensitive interfaces between the metal, substrate, and capping layer, the uses of the quantized metallic films for further ex-situ investigations and applications have been seriously limited. To this end, we develop a large-area fabrication method for continuous atomic-scale aluminum film. The self-limited oxidation of aluminum protects and quantizes the metallic film and enables ex-situ characterizations and device processing in air. Structure analysis and electrical measurements on the prepared films imply the quantum size effect in the atomic-scale aluminum film. Our work opens the way for further physics studies and device applications using the quantized electronic states in metals. (C) 2017 Author(s).
Characterization of Single-Crystalline Aluminum Thin Film on (100) GaAs Substrate
(2013-04-01)
Lin, Shi-Wei
;
Wu, Jau-Yang
;
Lin, Sheng-Di
;
Lo, Ming-Cheng
;
Lin, Ming-Huei
We have studied the structure and physical properties of an aluminum thin film grown on a (100) GaAs substrate. The X-ray diffraction (XRD) data shows that the Al film grown in situ by molecular beam epitaxy (MBE) is single crystalline. Compared with the polycrystalline film ex situ evaporated using an electron-gun (E-gun), the MBE-grown Al film has a high optical reflectivity in the visible and ultraviolet (UV) regime. In addition, the MBE-grown film has a 2-order-lower residue resistance, a 1-order-higher temperature coefficient of resistance, and a 2-order-larger magnetoresistance (MR) than the polycrystalline film. Owing to the long mean free time, the bulk-like electron-to-hole transition of Hall resistivity is observed for the first time in a nanoscale metal thin film. Our results suggest that MBE-grown Al thin films have great potential applications in metal-based nanoelectronics and nanophotonics. (C) 2013 The Japan Society of Applied Physics
Diamagnetic Response of Exciton Complexes in Semiconductor Quantum Dots
(2008-12-31)
Tsai, Ming-Fu
;
Lin, Hsuan
;
Lin, Chia-Hsien
;
Lin, Sheng-Di
;
Wang, Sheng-Yun
We report measurements of diamagnetic shifts for different exciton complexes confined in small InAs quantum dots. The measured diamagnetic responses are sensitive to the number of carriers in the exciton complexes, with systematic differences between neutral excitons, biexcitons, and trions. Theoretical calculations suggest that such systematic differences arise from very different extents of electron and hole wave functions confined in small quantum dots. The measured magnetic response of Coulomb energies is found to vary with the cube of the wave function extent, and can be a sensitive probe to the electron-hole wave function asymmetry.
Discrete monolayer light emission from GaSb wetting layer in GaAs
(2007-06-11)
Lo, Ming-Cheng
;
Huang, Shyh-Jer
;
Lee, Chien-Ping
;
Lin, Sheng-Di
;
Yen, Shun-Tung
Distinct light emission peaks from monolayers of GaSb quantum wells in GaAs were observed. Discrete atomic layers of GaSb for the wetting layer prior to quantum dot formation give rise to transition peaks corresponding to quantum wells with 1, 2, and 3 ML. From the transition energies the authors were able to deduce the band offset parameter between GaSb and GaAs. By fitting the experimental data with the theoretical calculated result using an 8x8 k center dot p Burt's Hamiltonian along with the Bir-Picus deformation potentials, the strain-free (fully strained) valence band discontinuity for this type-II heterojunction was determined to be 0.45 eV (0.66 eV). (c) 2007 American Institute of Physics.
Growth of atomic-scale aluminum film on GaAs substrate
(2016)
Lo, Ming-Cheng
;
Fan, Yen-Ting
;
Wu, Chu-Chun
;
Chen, Peng-Yu
;
Lin, Sheng-Di
We present the method for large-area growth of single-crystalline Al films in atomic scale on GaAs substrate by using molecular beam epitaxy. The grown Al film of thickness down to 5 nm exhibits smooth surface morphology, a clear and single X-ray diffraction peak in. theta-2 theta scan, and nearly transparent optical response. This work open a window for ex-situ studying quantum size effect in metal film.
Long-Wavelength Quantum-Dot Infrared Photodetectors With Operating Temperature Over 200 K
(2009-01-01)
Ling, Hong-Shi
;
Wang, Shiang-Yu
;
Lee, Chien-Ping
;
Lo, Ming-Cheng
;
電子工程學系及電子研究所
We demonstrate the high-temperature operation of confinement enhanced dots-in-a-well (CE-DWELL) quantum-dot infrared photodetectors (QDIPs). The thin Al(0.3)Ga(0.7)As barrier layer added above the InAs QDs greatly improve the lateral confinement of QD states in the In(0.15)Ga(0.85)M DWELL structure and the device performance. With better device parameters of CE-DWELL, it is possible to achieve high quantum efficiency, high operating temperature, and long-wavelength detection at the same time.
Strong coupling of different cavity modes in photonic molecules formed by two adjacent microdisk microcavities
(2010-11-08)
Lin, Hsuan
;
Chen, Jhih-Hao
;
Chao, Shih-Shing
;
Lo, Ming-Cheng
;
Lin, Sheng-Di
Strong couplings between cavity modes in photonic molecules formed by two preselected nearly identical microdisk microcavities with embedded quantum dots are investigated. By continuously tuning the refractive index of one microdisk, clear anticrossings in the resonant peak energies associated with crossings in the peak linewidths can be observed. The coupling strengths are extracted by the coupled mode theory and analyzed by the model considering the effective potential confining the electromagnetic waves in the microcavities. (C) 2010 Optical Society of America
Strong coupling of different cavity modes in photonic molecules formed by two adjacent microdisk microcavities
(2010-11-08)
Lin, Hsuan
;
Chen, Jhih-Hao
;
Chao, Shih-Shing
;
Lo, Ming-Cheng
;
Lin, Sheng-Di
Strong couplings between cavity modes in photonic molecules formed by two preselected nearly identical microdisk microcavities with embedded quantum dots are investigated. By continuously tuning the refractive index of one microdisk, clear anticrossings in the resonant peak energies associated with crossings in the peak linewidths can be observed. The coupling strengths are extracted by the coupled mode theory and analyzed by the model considering the effective potential confining the electromagnetic waves in the microcavities. (C) 2010 Optical Society of America
Vertically Coupled Quantum-Dot Infrared Photodetectors
(2010-06-01)
Lo, Ming-Cheng
;
Wang, Shiang-Yu
;
Ling, Hong-Shi
;
Lee, Chien-Ping
;
電子工程學系及電子研究所
Vertically coupled InAs-GaAs quantum-dot infrared photodetectors (QDIPs) were studied in this letter. With vertically coupled quantum dots (QDs), the QDs in the same column share the same electronic states which remove the QD size variation effect in the growth direction and result in a narrow response band and higher peak quantum efficiency. The coupled states increase the capture probability and also facilitate the carrier flow among QD layers. The frequency response of vertically coupled QDIPs is much faster than that of the conventional ones.