Browsing by Author "Lo, Shun-Tsung"

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A delta-doped quantum well system with additional modulation doping
(2011)
Luo, Dong-Sheng
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Lin, Li-Hung
;
Su, Yi-Chun
;
Wang, Yi-Ting
;
Peng, Zai Fong
A delta-doped quantum well with additional modulation doping may have potential applications. Utilizing such a hybrid system, it is possible to experimentally realize an extremely high two-dimensional electron gas (2DEG) density without suffering inter-electronic-subband scattering. In this article, the authors report on transport measurements on a delta-doped quantum well system with extra modulation doping. We have observed a 0-10 direct insulator-quantum Hall (I-QH) transition where the numbers 0 and 10 correspond to the insulator and Landau level filling factor nu = 10 QH state, respectively. In situ titled-magnetic field measurements reveal that the observed direct I-QH transition depends on the magnetic component perpendicular to the quantum well, and the electron system within this structure is 2D in nature. Furthermore, transport measurements on the 2DEG of this study show that carrier density, resistance and mobility are approximately temperature (T)-independent over a wide range of T. Such results could be an advantage for applications in T-insensitive devices.
A gate-free monolayer WSe2 pn diode
(2018-08-07)
Chen, Jhih-Wei
;
Lo, Shun-Tsung
;
Ho, Sheng-Chin
;
Wong, Sheng-Shong
;
Vu, Thi-Hai-Yen
Interest in bringing p- and n-type monolayer semiconducting transition metal dichalcogenides (TMD) into contact to form rectifying pn diode has thrived since it is crucial to control the electrical properties in two-dimensional (2D) electronic and optoelectronic devices. Usually this involves vertically stacking different TMDs with pn heterojunction or, laterally manipulating carrier density by gate biasing. Here, by utilizing a locally reversed ferroelectric polarization, we laterally manipulate the carrier density and created a WSe2 pn homojunction on the supporting ferroelectric BiFeO3 substrate. This non-volatile WSe2 pn homojunction is demonstrated with optical and scanning probe methods and scanning photoelectron microspectroscopy. A homo-interface is a direct manifestation of our WSe2 pn diode, which can be quantitatively understood as a clear rectifying behavior. The non-volatile confinement of carriers and associated gate-free pn homojunction can be an addition to the 2D electron-photon toolbox and pave the way to develop laterally 2D electronics and photonics.
Controllable Disorder in a Hybrid Nanoelectronic System: Realization of a Superconducting Diode
(2013-07-24)
Lo, Shun-Tsung
;
Chen, Kuang Yao
;
Lin, Sheng-Di
;
Wu, J-Y.
;
Lin, T. L.
We have studied a hybrid nanoelectronic system which consists of an AlGaAs/GaAs two-dimensional electron gas (2DEG) in close proximity (similar to 70 nm) to an Al superconducting nanofilm. By tuning the current through the Al film, we can change the conductance of the 2DEG and furthermore vary the effective disorder in the Al superconducting film in a controllable way. When a high current is injected into the film, screening which couples the Al film and the 2DEG results in a collapse of anti-symmetric behavior in the current-voltage characteristics, V(I) similar to - V(-I), which holds true in a conventional superconductor. Our results may open a new avenue of experimentally realizing a superconducting diode.
Crossover from negative to positive magnetoresistance in a Si delta-doped GaAs single quantum well
(2010-07-01)
Lo, Shun-Tsung
;
Chen, Kuang Yao
;
Su, Yi-Chun
;
Liang, C. -T.
;
Chang, Y. H.
We have performed magnetoresistance measurements on a Si delta-doped GaAs single quantum well With increasing temperature T, a crossover from negative magnetoresistance (NMR) to positive magnetoresistance (PMR) can be observed Our experimental results suggest that such a crossover corresponds to a transition from variable range hopping regime to activated electron transport. This is also consistent with the measured non-monotonic carrier density dependence on T. (C) 2010 Elsevier Ltd All rights reserved.
Insulating state to quantum Hall-like state transition in a spin-orbit-coupled two-dimensional electron system
(2014-07-07)
Lo, Shun-Tsung
;
Hsu, Chang-Shun
;
Lin, Y. M.
;
Lin, S-D
;
Lee, C. P.
We study interference and interactions in an InAs/InAsSb two-dimensional electron system. In such a system, spin-orbit interactions are shown to be strong, which result in weak antilocalization (WAL) and thereby positive magnetoresistance around zero magnetic field. After suppressing WAL by the magnetic field, we demonstrate that classical positive magnetoresistance due to spin-orbit coupling plays a role. With further increasing the magnetic field, the system undergoes a direct insulator-quantum Hall transition. By analyzing the magnetotransport behavior in different field regions, we show that both electron-electron interactions and spin-related effects are essential in understanding the observed direct transition. (C) 2014 AIP Publishing LLC.
Magnetotransport in an aluminum thin film on a GaAs substrate grown by molecular beam epitaxy
(2011)
Lo, Shun-Tsung
;
Chuang, Chiashain
;
Lin, Sheng-Di
;
Chen, Kuang Yao
;
Liang, Chi-Te
Magnetotransport measurements are performed on an aluminum thin film grown on a GaAs substrate. A crossover from electron- to hole-dominant transport can be inferred from both longitudinal resistivity and Hall resistivity with increasing the perpendicular magnetic field B. Also, phenomena of localization effects can be seen at low B. By analyzing the zero-field resistivity as a function of temperature T, we show the importance of surface scattering in such a nanoscale film.
On the direct insulator-quantum Hall transition in two-dimensional electron systems in the vicinity of nanoscaled scatterers
(2011)
Liang, Chi-Te
;
Lin, Li-Hung
;
Chen, Kuang Yao
;
Lo, Shun-Tsung
;
Wang, Yi-Ting
A direct insulator-quantum Hall (I-QH) transition corresponds to a crossover/transition from the insulating regime to a high Landau level filling factor nu > 2 QH state. Such a transition has been attracting a great deal of both experimental and theoretical interests. In this study, we present three different two-dimensional electron systems (2DESs) which are in the vicinity of nanoscaled scatterers. All these three devices exhibit a direct I-QH transition, and the transport properties under different nanaoscaled scatterers are discussed.
Probing the onset of strong localization and electron-electron interactions with the presence of a direct insulator-quantum Hall transition
(2010-10-01)
Lo, Shun-Tsung
;
Chen, Kuang Yao
;
Lin, T. L.
;
Lin, Li-Hung
;
Luo, Dong-Sheng
We have performed low-temperature transport measurements on a disordered two-dimensional electron system (2DES). Features of the strong localization leading to the quantum Hall effect are observed after the 2DES undergoes a direct insulator-quantum Hall transition on increasing the perpendicular magnetic field. However, such a transition does not correspond to the onset of strong localization. The temperature dependences of the Hall resistivity and Hall conductivity reveal the importance of the electron-electron interaction effects for the observed transition in our study. (C) 2010 Elsevier Ltd. All rights reserved.
Probing the onset of strong localization and electron-electron interactions with the presence of a direct insulator-quantum Hall transition
(2010-10-01)
Lo, Shun-Tsung
;
Chen, Kuang Yao
;
Lin, T. L.
;
Lin, Li-Hung
;
Luo, Dong-Sheng
We have performed low-temperature transport measurements on a disordered two-dimensional electron system (2DES). Features of the strong localization leading to the quantum Hall effect are observed after the 2DES undergoes a direct insulator-quantum Hall transition on increasing the perpendicular magnetic field. However, such a transition does not correspond to the onset of strong localization. The temperature dependences of the Hall resistivity and Hall conductivity reveal the importance of the electron-electron interaction effects for the observed transition in our study. (C) 2010 Elsevier Ltd. All rights reserved.
Spin-orbit-coupled superconductivity
(2014-06-25)
Lo, Shun-Tsung
;
Lin, Shih-Wei
;
Wang, Yi-Ting
;
Lin, Sheng-Di
;
Liang, C. -T.
Superconductivity and spin-orbit (SO) interaction have been two separate emerging fields until very recently that the correlation between them seemed to be observed. However, previous experiments concerning SO coupling are performed far beyond the superconducting state and thus a direct demonstration of how SO coupling affects superconductivity remains elusive. Here we investigate the SO coupling in the critical region of superconducting transition on Al nanofilms, in which the strength of disorder and spin relaxation by SO coupling are changed by varying the film thickness. At temperatures T sufficiently above the superconducting critical temperature T-c, clear signature of SO coupling reveals itself in showing a magneto-resistivity peak. When T < T-c, the resistivity peak can still be observed; however, its line-shape is now affected by the onset of the quasi two-dimensional superconductivity. By studying such magneto-resistivity peaks under different strength of spin relaxation, we highlight the important effects of SO interaction on superconductivity.
Tunable insulator-quantum Hall transition in a weakly interacting two-dimensional electron system
(2013-07-03)
Lo, Shun-Tsung
;
Wang, Yi-Ting
;
Lin, Sheng-Di
;
Strasser, Gottfried
;
Bird, Jonathan P.
We have performed low-temperature measurements on a gated two-dimensional electron system in which electron-electron (e-e) interactions are insignificant. At low magnetic fields, disorder-driven movement of the crossing of longitudinal and Hall resistivities (rho (xx) and rho (xy)) can be observed. Interestingly, by applying different gate voltages, we demonstrate that such a crossing at rho (xx) similar to rho (xy) can occur at a magnetic field higher, lower, or equal to the temperature-independent point in rho (xx) which corresponds to the direct insulator-quantum Hall transition. We explicitly show that rho (xx) similar to rho (xy) occurs at the inverse of the classical Drude mobility 1/mu (D) rather than the crossing field corresponding to the insulator-quantum Hall transition. Moreover, we show that the background magnetoresistance can affect the transport properties of our device significantly. Thus, we suggest that great care must be taken when calculating the renormalized mobility caused by e-e interactions.