Browsing by Author "Liu, HS"

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Bipolar photogenerated terahertz radiation in biased photoconductive switches
(2003-05-01)
Lin, PI
;
Luo, CW
;
Liu, HS
;
Wu, KH
;
Juang, JY
The characteristics of optically induced bipolar THz radiation in biased photoconductive switches were investigated systematically by using free-space electro-optic sampling technique. The emitted radiation shows nearly symmetrical waveform with broadband frequency spectrum spanning over 0.1-3 THz. It was observed that the bipolar nature and the emitted frequency spectrum distribution remained unchanged on varying the optical excitation fluence, strength of biased field and the emitter gap spacing. The dynamics of emitted THz transient are in agreement with the optically induced ultrafast charge transport process driven by the biased field. (C) 2003 Elsevier Science B.V. All rights reserved.
Characterizations of deep levels in SnTe-doped GaSb by admittance spectroscopy
(1996-09-23)
Chen, JF
;
Chen, NC
;
Liu, HS
;
交大名義發表
;
電子物理學系
A dominant deep level with an activation energy of 0.23-0.26 eV was observed by admittance spectroscopy for SnTe-doped GaSb layers grown directly on GaAs substrates by molecular beam epitaxy (MBE). The activation energy and capture cross section of the deep level are similar to the levels detected in S-doped and Te-doped GaSb grown by MBE, indicating that this deep level originates either from a native defect or a common impurity in n-type GaSb. The Sb-4/Ga flux ratio was found to affect the Hall mobility and concentration of the deep level in a similar way, with an optimal beam equivalent pressure ratio around 7 obtained for GaSb grown at 550 degrees C, which should correspond to the lowest ratio to maintain a Sb-stabilized surface reconstruction. Analysis of this result suggests that the deep level seen by us is a complex defect. (C) 1996 American Institute of Physics.
Characterizations of deep levels in SnTe-doped GaSb by admittance spectroscopy
(1996-09-23)
Chen, JF
;
Chen, NC
;
Liu, HS
;
電子物理學系
;
Department of Electrophysics
A dominant deep level with an activation energy of 0.23-0.26 eV was observed by admittance spectroscopy for SnTe-doped GaSb layers grown directly on GaAs substrates by molecular beam epitaxy (MBE). The activation energy and capture cross section of the deep level are similar to the levels detected in S-doped and Te-doped GaSb grown by MBE, indicating that this deep level originates either from a native defect or a common impurity in n-type GaSb. The Sb-4/Ga flux ratio was found to affect the Hall mobility and concentration of the deep level in a similar way, with an optimal beam equivalent pressure ratio around 7 obtained for GaSb grown at 550 degrees C, which should correspond to the lowest ratio to maintain a Sb-stabilized surface reconstruction. Analysis of this result suggests that the deep level seen by us is a complex defect. (C) 1996 American Institute of Physics.
Deep levels in SnTe-doped GaSb grown on GaAs by molecular beam epitaxy
(1996-07-01)
Chen, JF
;
Chen, NC
;
Liu, HS
;
交大名義發表
;
電子物理學系
A dominant deep level with an activation energy of 0.23-0.26 eV was observed by admittance spectroscopy in SnTe-doped GaSb layers grown directly on GaAs substrates by molecular beam epitaxy (MBE). The Sb-4/Ga Bur ratio was found to affect the Hall mobility and the concentration of the deep level in a similar way, with an optimal beam equivalent pressure ratio of around 7 obtained for GaSb grown at 550 degrees C, which should correspond to the lowest ratio at which a Sb-stabilized surface reconstruction can be maintained. This electron level is commonly detected in n-type (SnTe-, S- and Te-doped) GaSb, but not in undoped p-type GaSb, suggesting that the level is not a simple native defect, but may be connected with the impurity used for n-type doping of GaSb.
Deep levels, electrical and optical characteristics in SnTe-doped GaSb Schottky diodes
(1996-11-01)
Chen, JF
;
Chen, NC
;
Liu, HS
;
交大名義發表
;
電子物理學系
The GaSb layers investigated were grown directly on GaAs substrates by molecular beam epitaxy (MBE) using SnTe source as the n-type dopant. By using admittance spectroscopy, a dominant deep level with the activation energy of 0.23-0.26 eV was observed and its concentration was affected by the Sb-4/Ga flux ratio in the MBE growth. A lowest deep-level concentration together with a highest mobility was obtained for GaSb grown at 550 degrees C under a Sb-4/Ga beam equivalent pressure (BEP) ratio around 7, which should correspond to the lowest ratio to maintain a Sb-stabilized surface reconstruction. In the Hall measurement, an analysis of the temperature-dependent mobility shows that the ionized impurity concentration increases proportionally with the sample's donor concentration, suggesting that the ionized impurity was introduced by an SnTe source. In addition, optical properties of an undoped p-, a lightly and heavily SnTe-doped GaSb layers were studied by comparing their photoluminesence spectra at 4.5K.
Deep levels, electrical and optical characteristics in SnTe-doped GaSb Schottky diodes
(1996-11-01)
Chen, JF
;
Chen, NC
;
Liu, HS
;
電子物理學系
;
Department of Electrophysics
The GaSb layers investigated were grown directly on GaAs substrates by molecular beam epitaxy (MBE) using SnTe source as the n-type dopant. By using admittance spectroscopy, a dominant deep level with the activation energy of 0.23-0.26 eV was observed and its concentration was affected by the Sb-4/Ga flux ratio in the MBE growth. A lowest deep-level concentration together with a highest mobility was obtained for GaSb grown at 550 degrees C under a Sb-4/Ga beam equivalent pressure (BEP) ratio around 7, which should correspond to the lowest ratio to maintain a Sb-stabilized surface reconstruction. In the Hall measurement, an analysis of the temperature-dependent mobility shows that the ionized impurity concentration increases proportionally with the sample's donor concentration, suggesting that the ionized impurity was introduced by an SnTe source. In addition, optical properties of an undoped p-, a lightly and heavily SnTe-doped GaSb layers were studied by comparing their photoluminesence spectra at 4.5K.
On the origin of photogenerated terahertz radiation from current-biased superconducting YBa2Cu3O7-delta thin films
(2004-06-15)
Lin, PI
;
Luo, CW
;
Liu, HS
;
Chen, SF
;
Wu, KH
The origin of photogenerated terahertz radiation pulse emitted from current-biased superconducting YBa2Cu3O7-delta thin films excited by femtosecond optical laser pulses is delineated. By investigating the performance of the transient terahertz radiation generated under different operating parameters, pulse reshaping in the measured terahertz electric field caused by the kinetic inductance of the superconducting charge carriers is identified. After recovering the original wave forms of the emitted terahertz pulses, the transient supercurrent density directly correlated to the optically excited quasiparticle dynamics is obtained. A fast decreasing component of about 1.0 ps and a slower recovery process with a value of 2.5 ps are unambiguously delineated in the optically induced supercurrent modulation. The radiation mechanism of the transient terahertz pulse related to nonequilibrium superconductivity is discussed. (C) 2004 American Institute of Physics.