Browsing by Author "WANG, C"

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2-DIMENSIONAL ELECTRON GASES IN DELTA-DOPED GAAS/IN0.25GA0.75AS/GAAS HETEROSTRUCTURES
(1991-06-10)
LIN, W
;
HSU, WC
;
WU, TS
;
CHANG, SZ
;
WANG, C
Delta-doped (delta-doped) GaAs/In0.25Ga0.75As/GaAs strained-layer modulation-doped field-effect transistor (delta-SMODFET) structures grown by the low-pressure metalorganic chemical vapor deposition (LP-MOCVD) technique have been studied for the first time. The delta-doped GaAs, adopted as the electron supplier, was obtained by a stop-growth process so that a very thin and heavily doped layer (1.9 X 10(13) cm-2) can be realized. Experimental results show that a structure with an 80 angstrom In0.25Ga0.75As layer as the active channel and an 80 angstrom spacer layer demonstrated the highest two-dimensional electron gases mobility of 26 800 cm2/V s. This structure is easy to achieve by the LP-MOCVD method because the growth of AlGaAs is avoided and is promising for high performance FETs.
DOUBLE RESONANT BEHAVIOR OF MICROSTRIP RING-RESONATOR IN TL-BASED HIGH T-C SUPERCONDUCTING FILMS
(1994-12-19)
WU, SC
;
YEH, CY
;
CHEN, FH
;
TSENG, TY
;
WANG, C
EFFECT OF SN ON THE SUPERCONDUCTIVITY OF THE DYBA2CU3O7-DELTA SYSTEM
(1989-12-01)
WANG, C
;
CHEN, LT
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CHANG, HL
;
CHU, ML
;
HSU, FW
EFFECTS OF ZRO2 ON THE TEXTURING AND PROPERTIES OF MELT-PROCESSED Y1BA2CU3O7-DELTA
(1994-04-25)
JUANG, JY
;
WU, CL
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WANG, SJ
;
CHU, ML
;
WU, KH
The addition of ZrO2 is found to be very effective as the nucleation sites to promote the oriented growth of Y1Ba2Cu3O7-delta (YBCO) during peritectic solidification. Extended regions of well-textured YBCO grains with superior superconducting properties of the YBCO bulk are readily obtained by a single-step melt process at much lower process temperatures. At 77 K, the platelike Josephson weak-link behaviors observed in pure melt-processed YBCO have been effectively eliminated, indicating that the coherency between the spherulitic superconducting YBCO grains may have been greatly improved by ZrO2 additions.
LOW-FIELD SCALING BEHAVIORS OF GLOBAL FLUX PINNING IN TL-BA-CA-CU-O THIN-FILMS
(1992-07-01)
JUANG, JY
;
WANG, SJ
;
UEN, TM
;
GOU, YS
;
CHANG, HL
The scaling behaviors of global pinning force density (F(p) = J(c) X B) in dc sputtered TI-Ba-Ca-Cu-0 superconducting thin films as functions of both the reduced magnetic field and temperature were investigated by direct transport measurements for fields up to 4 kOe. It was found that, depending on the film granularities (originating from different deposition and annealing conditions and characterized by the temperature and magnetic-field dependencies of critical currents), vastly different scaling behaviors were manifested. For films with very high critical current densities, where the intragranular behaviors prevailed, the conventional surface core pinning by some high-density normal pinning centers combined with a significant flux creep appeared to be the predominant limiting mechanisms for the critical current densities, whereas in more granular films, suggestive collective-pinning effects arising from the weakly pinned fluxoids in the intergranular networks were observed.
PREPARATION OF TL2CA2BA2CU3OX SUPERCONDUCTING THIN-FILMS BY DC SPUTTERING
(1989-04-01)
CHANG, HL
;
WANG, C
;
CHU, ML
;
UEN, TM
;
GOU, YS
SYNTHESIS PROCESS OF THE HIGH-TC SUPERCONDUCTOR IN THE TL2CA2BA2CU3OX PHASE
(1989-04-01)
WANG, C
;
CHANG, HL
;
CHU, ML
;
GOU, YS
;
UEN, TM
THE DELTA-DOPED IN0.25GA0.75AS/GAAS PSEUDOMORPHIC HIGH ELECTRON-MOBILITY TRANSISTOR STRUCTURES PREPARED BY LOW-PRESSURE METAL ORGANIC-CHEMICAL VAPOR-DEPOSITION
(1991-06-01)
CHANG, CY
;
LIN, W
;
HSU, WC
;
WU, TS
;
CHANG, SZ
The (800 angstrom)GaAs/In0.25Ga0.75As/(0.5-mu-m) GaAs strain layers with delta-doping in the GaAs cap layer were fabricated without using AlGaAs layers. Triethylgallium (TEG), trimethylindium (TMI), arsine (AsH3) and silane (SiH4) were used as the sources and dopants in these structures grown by the low-pressure metalorganic chemical vapor deposition (LP-MOCVD) technique for the first time to study these structures. The delta-doping was obtained by a stop-growth process by which a very thin and heavily doped layer (1.86 x 10(13) cm-2) can be realized. For the (delta-doped) GaAs/In0.25Ga0.75As/GaAs high electron mobility transistor (HEMT) structures, the concentration of two-dimensional electron gas (2-DEG) and the Hall mobilities were investigated. Experimental results show that a structure with (80 angstrom) In0.25Ga0.75As as the active channel and with a 70 angstroms spacer layer revealed the highest 2-DEG concentration and mobility product of 5.5 x 10(16) V-1.s-1 at a temperature of 77 K. These structures are easy to achieve by the LP-MOCVD mechod and are promising for high-performance field effect transistors (FETs).
THE MAGNETIC AND TRANSPORT-PROPERTIES OF HIGH-CRITICAL-CURRENT TL2BA2CA2CU3OX SUPERCONDUCTING THIN-FILMS
(1991-08-26)
CHU, ML
;
CHANG, HL
;
WANG, C
;
JUANG, JY
;
UEN, TM
Highly c-axis-oriented Tl2Ba2Ca2Cu3O(x) superconducting thin films with the critical current density as high as 1 X 10(7) A/cm2 at 87 K were obtained by single-target dc sputtering on LaAlO3 (100) substrates followed by encapsulated compensate annealing. The strong linear temperature dependence of zero-field critical current at low temperatures suggests a creep-dominated behavior. Preliminary field dependence studies on the critical current density in low-field regime (< 2 kOe) shows no evidence of hysteresis commonly encountered in films with higher granularity. The scaling behavior of the global pinning force density exhibits strong resemblance to conventional type-II superconductors with the pinning force density of the same order of magnitude as that in strong pinned NbN thin films.
THE SCALING BEHAVIORS OF PINNING IN TLBACACUO SUPERCONDUCTING THIN-FILMS
(1992-08-01)
CHANG, HL
;
WANG, C
;
JUANG, JY
;
UEN, TM
;
GOU, YS
The scaling behaviors of global pinning force density in dc sputtered TlBaCaCuO superconducting thin films as functions of both reduced magnetic fields and temperatures were investigated by direct transport measurements with applied fields perpendicular to the film surface. The pinning mechanisms which were depicted by the scaling behaviors of the Tl-based thin films were found to be strongly dependent on the superconducting properties of the films. For films with high critical current densities the conventional flux line shear pinning appeared to be the predominant limiting mechanism for the current carrying capability. Whereas in more granular film that did not scale well when normalized by the extrapolated Hc2, an astonishing scaling behavior by taking a reversible field H* as the normalization parameters was observed.