Browsing by Author "Tu, SL"

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Alterable temperature-dependent wavelength shifts in (InP)(2)/(GaP)(2) quantum wells
(1998-02-02)
Cheng, YC
;
Tai, K
;
Chou, ST
;
Huang, KF
;
Tu, SL
Alterable temperature-dependent emission wavelength shifts were observed from (InP)(2)/(GaP)(2) short-period superlattices (SPSs) quantum wells grown with different interruption periods. Photoluminescence spectra showed that the peak energy of the SPS samples is inversely proportional to the interruption time conducted between the two consecutive binary growth sequences in the SPS regions. It is believed that a lateral composition modulation occurred during the interruption period which resulted in periodic In-rich and Ga-rich regions in the SPS quantum wells along the growth plane. With the lateral compositional variation, temperature variation can induce a multiaxial strain effect which can either amplify or reduce the temperature-dependent wavelength shift of the SPS quantum wells with different interruption periods. (C) 1998 American Institute of Physics.
Characteristics of nonalloyed pseudomorphic high electron mobility transistors using InAs/InxGa1-xAs (x=-> 0) AlyGa1-yAs (y=0 -> 0.3) contact structures
(1997-06-01)
Chen, SS
;
Lin, CC
;
Lan, WH
;
Tu, SL
;
Peng, CK
A molecular beam epitaxy InAs/InxGa1-xAs (x = 1 --> 0)/AlyGa1-yAs (y = 0 --> 0.3) heterojunction was used as an ohmic contact structure to the GaAs-based pseudomorphic high electron mobility transistors (PHEMTs). This nonalloyed PHEMT had a specific contact resistance r(c) of 1.05 x 10(-7) Omega . cm(2) and an extrinsic transconductance g(me) of 272 mS/mm for devices with 1 mu m gate-length, microwave measurements shelved a current gain cut-off frequency f(t) of 22 GHz and a maximum oscillation frequency f(max) of 43 GHz. These results are comparable to our best conventional PHEMTs' alloyed at 450 degrees C and 2 min duration. Meanwhile, a small-signal equivalent circuit model of the nonalloyed PHEMT has also been demonstrated.
Characteristics of nonalloyed pseudomorphic high electron mobility transistors using InAs/InxGa1-xAs (x=-> 0) AlyGa1-yAs (y=0 -> 0.3) contact structures
(1997-06-01)
Chen, SS
;
Lin, CC
;
Lan, WH
;
Tu, SL
;
Peng, CK
A molecular beam epitaxy InAs/InxGa1-xAs (x = 1 --> 0)/AlyGa1-yAs (y = 0 --> 0.3) heterojunction was used as an ohmic contact structure to the GaAs-based pseudomorphic high electron mobility transistors (PHEMTs). This nonalloyed PHEMT had a specific contact resistance r(c) of 1.05 x 10(-7) Omega . cm(2) and an extrinsic transconductance g(me) of 272 mS/mm for devices with 1 mu m gate-length, microwave measurements shelved a current gain cut-off frequency f(t) of 22 GHz and a maximum oscillation frequency f(max) of 43 GHz. These results are comparable to our best conventional PHEMTs' alloyed at 450 degrees C and 2 min duration. Meanwhile, a small-signal equivalent circuit model of the nonalloyed PHEMT has also been demonstrated.
Growth and fatigue properties of pulsed laser deposited Pb1-xLax(ZryTiz)O-3 thin films with [001] preferred orientation
(1996-12-01)
Lin, WJ
;
Tseng, TY
;
Wu, YZ
;
Lin, SP
;
Tu, SL
Growth of [00/] preferentially oriented Pb1-xLax(ZryTiz) O-3 (PLZT) thin films was carried out by using targets of either tetragonal or rhombohedral structure. The tetragonal films grew in a similar manner to the rhombohedral films. Both the substrate temperature (500 or 550 degrees C) and oxygen pressure (0.1 mbar, 10 Pa) required stringent control in order to deposit [00/]-textured PLZT thin films. The ferroelectric and fatigue properties were examined. The films deposited on YBa2Cu3O7-x and CeO2 coated silicon (YBCO/CeO2/Si) substrates possessed substantially lower remanent polarization than those grown on YBCO coated SrTiO3 (YBCO/STO) substrates; this is ascribed to inferior crystallinity of the PLZT/BCO/CeO2/Si films. The remanent polarization of tetragonal PLZT films was degraded insignificantly up to 10(8) polarization switching cycles, whereas that of rhombohedral PLZT films was already reduced to 80% of the initial value after 10(8) cycles. Low endurance of rhombohedral films was ascribed to the periodic stress induced when the inclined spontaneous polarization vector (P=[111]) switched. On the other hand, high endurance of tetragonal films was explained by the fact that the spontaneous polarization vector (P=[001]) lies along the film's normal such that switch cycles cause no lateral stress.
High performance non-alloyed pseudomorphic high electron mobility transistors
(1996-07-01)
Peng, CK
;
Lan, WH
;
Tu, SL
;
Yang, SJ
;
Chen, SS
We have studied the InAs/GaAs strained layer superlattice (SLS) structures as non-alloyed contacts applied to pseudomorphic high electron mobility transistors (PHEMTs) grown by the molecular beam epitaxy (MBE) system. Transmission line measurements with four point configurations showed that specific contact resistances between 6.6 x 10(-7) and 2.6 x 10(-6) Omega cm(2) were obtained for the as-grown devices, with a linear correlation coefficient of 0.997. D.c. measurements of the as-grown PHEMT with 1 mu m gate showed a transconductance of 240 ms mm(-1). Microwave measurements on the same device showed a cut-off frequency of 19 GHz and a maximum power gain frequency of 42 GHz. These results are comparable with those of devices with the conventional contact scheme. Meanwhile, since the non-alloying process maintains excellent surface morphology and sharp metal pad edges, AuGeNi type metals can be used in small dimension devices. In contrast, the conventionally alloyed devices showed rough surface morphology and zigzag edges, which may affect device processing and limit the usefulness of AuGeNi metal as the ohmic contact in small dimension devices.
Influence of crystal structure on the fatigue properties of Pb1-xLax(Zr-y,Ti-z)O-3 thin films prepared by pulsed-laser deposition technique
(1997-05-01)
Lin, WJ
;
Tseng, TY
;
Lin, SP
;
Tu, SL
;
Chang, H
Lead lanthanum zirconate titanate (Pb1-xLax(Zr-y,Ti-z)O-3, PLZT) films containing [00l] preferentially oriented grains were produced successfully on YBa2Cu3O7-x-coated (YBCO-coated) SrTiO3, (STO) or YBCO/CeO2-coated silicon substrates; films containing randomly oriented grains were created on platinum-coated silicon substrates. The latter possessed significantly inferior ferroelectric properties, a fact ascribed to the presence of a paraelectric phase (TiO2,) at the PLZT/platinum interface. On the other hand, the PLZT/YBCO/STO films exhibited better electrical properties than did the PLZT/YBCO/CeO2/Si films, and this phenomenon was attributed to better alignment of the grains in normal and in-plane orientations. In terms of fatigue properties, the [00l] textured films that were deposited on YBCO/CeO2/Si substrates possessed substantially superior polarization-switching-cycle endurance versus the randomly oriented films grown on Pt(Ti)/Si substrates. Moreover, the tetragonal films behaved much more satisfactorily than did the rhombohedral PLZT films. The ferroelectric parameters of tetragonal PLZT films showed no significant degradation up to 10(9) polarization switching cycles, whereas the remnant polarization and coercive force of the rhombohedral PLZT films had already degraded to 80% of their initial values after 10(8) cycles.
Influence of crystal structure on the fatigue properties of Pb1-xLax(Zr-y,Ti-z)O-3 thin films prepared by pulsed-laser deposition technique
(1997-05-01)
Lin, WJ
;
Tseng, TY
;
Lin, SP
;
Tu, SL
;
Chang, H
Lead lanthanum zirconate titanate (Pb1-xLax(Zr-y,Ti-z)O-3, PLZT) films containing [00l] preferentially oriented grains were produced successfully on YBa2Cu3O7-x-coated (YBCO-coated) SrTiO3, (STO) or YBCO/CeO2-coated silicon substrates; films containing randomly oriented grains were created on platinum-coated silicon substrates. The latter possessed significantly inferior ferroelectric properties, a fact ascribed to the presence of a paraelectric phase (TiO2,) at the PLZT/platinum interface. On the other hand, the PLZT/YBCO/STO films exhibited better electrical properties than did the PLZT/YBCO/CeO2/Si films, and this phenomenon was attributed to better alignment of the grains in normal and in-plane orientations. In terms of fatigue properties, the [00l] textured films that were deposited on YBCO/CeO2/Si substrates possessed substantially superior polarization-switching-cycle endurance versus the randomly oriented films grown on Pt(Ti)/Si substrates. Moreover, the tetragonal films behaved much more satisfactorily than did the rhombohedral PLZT films. The ferroelectric parameters of tetragonal PLZT films showed no significant degradation up to 10(9) polarization switching cycles, whereas the remnant polarization and coercive force of the rhombohedral PLZT films had already degraded to 80% of their initial values after 10(8) cycles.
Optical image recognition using photorefractive crystal plates
(1997)
Hsieh, ML
;
Lin, SH
;
Hsu, KY
;
Hsieh, TC
;
Lin, SP
We demonstrate a real-time optical image recognition system using photorefractive thin plates. The effects of donor/acceptor concentration ratio in thin lithium niobate crystal plates on the photorefractive response time and the grating diffraction efficiency are presented.
Ordering reduction in In0.5Ga0.5P grown by solid source molecular beam epitaxy
(1998-02-15)
Cheng, YC
;
Tai, KC
;
Chou, ST
;
Huang, KF
;
Tu, SL
In0.5Ga0.5P grown on GaAs substrates with different tilting angles by solid source molecular beam epitaxy (SSMBE) is studied. The results showed that a weak ordering effect still exists in SSMBE grown epilayers with tilted substrates. However, the ordering effect can be drastically reduced by growing In0.5Ga0.5P on a 15 degrees tilted substrate with an InAlP/InGaP superlattices (SL) buffer layer. The In0.5Ga0.5P epilayer grown by this method showed a peak photoluminescence (PL) energy of similar to 1.91 eV at room temperature, which is similar to the reported value for a fully disordered sample. The intensity of the ordering effect is characterized by polarized PL spectroscopy, and the reduction in the ordering intensity is attributed to the elimination of initial surface strain by the SL buffer layer.
Sputtered Cr and reactively sputtered CrNx serving as barrier layers against copper diffusion
(1998-12-01)
Chuang, JC
;
Tu, SL
;
Chen, MC
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The barrier capability of sputter deposited Cr and reactively sputter deposited CrNx films against Cu diffusion in a structure of Cu/barrier/p(+)n junction diodes was investigated by means of thermal annealing at elevated temperatures in conjunction with electrical measurements and material analysis. For a 500 Angstrom thick barrier layer, the barrier capability of a pure Cr layer was limited to temperatures up to 500 degrees C, while CrNx films sputter deposited in a gas mixture of Ar and N-2 showed improved barrier capabilities. With Ar/N-2 flow rates of 24/6 to 24/12 standard cubic centimeters per minute, the deposited CrNx films possessed a much improved barrier capability. In particular, the Cu/CrNx (24/9)/p(+)n junction diodes were capable of sustaining 30 min of thermal anneal at temperatures up to 700 degrees C without degradation of the diodes' electrical characteristics. The failure of Cu/Cr/p(+)n and Cu/CrNx/p(+)n junction diodes under extreme thermal treatment was presumed to arise from two mechanisms: grain boundary diffusion for lightly nitrogen doped CrNx and pure Cr barriers, and localized defect (microcrack) diffusion for excessively nitrogen doped CrNx barriers.