Browsing by Author "TSAI, KL"

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2-COLOR INFRARED PHOTODETECTOR USING GAAS/ALGAAS AND STRAINED INGAAS/ALGAAS MULTIQUANTUM WELLS
(1993-06-28)
TSAI, KL
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CHANG, KH
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LEE, CP
;
HUANG, KF
;
TSANG, JS
A two-color infrared detector using GaAs/A]GaAs and strained InGaAs/AlGaAs multiquantum wells is demonstrated. The response peak of the GaAs/AlGaAs quantum well is at 8 mum, and that of the InGaAs/AlGaAs quantum well is at 5.3 mum. The responsivity of the detector is 1 A/W at 8 mum and 0.27 A/W at 5.3 mum; these are the best values reported for a two-color quantum well infrared detectors (QWIPs) with peak sensitivities in the spectral regions of 3-5.3 mum and 7.5-14 mum. Single-colored 5.3 and 8 mum QWIPs were also fabricated to study the bias dependent behavior. This behavior can be explained using the concept of current continuity. Because of a higher electrical resistance, a high electric field domain is always formed first in the shorter wavelength quantum well stack.
2-COLOR QUANTUM-WELL INFRARED PHOTODETECTOR WITH PEAK SENSITIVITIES AT 3.9 MU-M AND 8.1 MU-M
(1994-08-04)
TSAI, KL
;
LEE, CP
;
TSANG, JS
;
CHEN, HR
;
電子工程學系及電子研究所
A two-colour infra-red photodetector using multistacks of GaAs/AlGaAs quantum wells is demonstrated. The response peaks are at 3.9 and 8.1 mum. The peak responsivities of the detector are 0.4A/W and 35mA/W for 8.1mum and 3.9mum bands, respectively. The detectivities of the 3.9 and 8.1 mum bands are 7.5 x 10(9) and 1.5 x 10(10)cmHz1/2/W. These values are the best reported results for two-colour detectors with peak sensitivities in the spectral regions of 3-5 and 8-12mum.
2-DIMENSIONAL BI-PERIODIC GRATING-COUPLED ONE-COLOR AND 2-COLOR QUANTUM-WELL INFRARED PHOTODETECTORS
(1995-02-01)
TSAI, KL
;
LEE, CP
;
TSANG, JS
;
CHEN, HR
;
CHANG, KH
Multiple quantum well infrared photodetectors (QWIP's) with two-dimensional bi-periodic grating couplers have been demonstrated. For one-color QWIP's, the response linewidths of such QWIP's are found to be much wider than those of conventional grating coupled QWIP's. The bi-periodic gratings have also been applied to two color QWIP's to separately optimize the absorption at two wavelength bands. The large difference in responsivities at the two wavelength bands for devices with single period gratings can be greatly reduced with the use of bi-periodic gratings.
ASYMMETRIC DARK CURRENT IN QUANTUM-WELL INFRARED PHOTODETECTORS
(1994-05-02)
TSAI, KL
;
LEE, CP
;
CHANG, KH
;
LIU, DC
;
CHEN, HR
Asymmetric dark current versus voltage characteristics in quantum weil infrared photodetectors have been studied. A model based on asymmetrical potential barriers was proposed. The asymmetrical potential barriers, which are most likely due to the accumulation of oxygen impurities at one of the interfaces, cause the asymmetrical I-V characteristics. The height of the potential spike is found to increase with the Al content in the AlGaAs barriers. Calculations based on our model agree well with experimental results.
COMPOSITION MODULATION OF INXGA1-XAS QUANTUM-WELLS BY FAST DIMER ARSENIC FLUX CHANGE USING VALVED ARSENIC CRACKER
(1994-01-01)
LIU, DC
;
LEE, CP
;
TSAI, KL
;
TSANG, JS
;
CHEN, HR
By fast change of the As-2 flux using a high temperature valved cracker, we have demonstrated the growth of strained InxGa1-xAs quantum wells with different compositions. The modulation of composition is due to the change in incorporation rates of the group III atoms under different As-2 fluxes. Photoluminescence (PL) emission from the quantum wells clearly indicates the change in composition. A change of In composition from 20.6% to 8.5%, has been achieved by changing the V/III beam-equivalent-pressure (BEP) ratio from 11.7 to 3.9. By this technique of composition modulation, we have fabricated strained InxGa1-xAs/GaAs single quantum well lasers with different emission wavelengths.
COMPOSITIONAL DISORDERING OF ALGAAS/GAAS SUPERLATTICES BY USING THE LOW-TEMPERATURE-GROWN GAAS
(1995-07-01)
TSANG, JS
;
LEE, CP
;
FAN, JC
;
TSAI, KL
;
CHEN, HR
The use of low-temperature (similar to 200 degrees C) grown GaAs by molecular beam epitaxy to induce compositional disordering of AlGaAs/GaAs superlattices has been studied. After furnace annealing between 700 and 850 degrees C for 30 min, an obvious blue shift in the peak wavelength of the superlattice emission is observed by the 77 K photoluminescence (PL), indicating that the emission has been changed from that of the GaAs quantum wells to that of the intermixed AlGaAs. The PL shift and the depth profile of Al concentration measured by secondary ion mass spectrometry indicate that the superlattice is nearly totally disordered after 850 degrees C annealing. (C) 1995 American Vacuum Society.
CURRENT GAINS OF ALAS/GAAS TUNNELING EMITTER BIPOLAR-TRANSISTORS WITH 25-500-ANGSTROM BARRIER THICKNESS
(1993-10-14)
CHEN, HR
;
LEE, CP
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CHANG, CY
;
TSAI, KL
;
TSANG, JS
The current gain of an AlAs/GaS tunnelling emitter bipolar transistor (TEBT) is found to increase monotonically with barrier thickness in the range 25-200 angstrom and fall off for barrier thickness increasing from 200 to 500 angstrom. It is found that a thicker barrier can suppress the base-to-emitter hole injection better and increase the current gain, but a barrier which is too thick decreases the current gain due to the suppression of the electron current.
EFFECTS OF LOW-TEMPERATURE-GROWN GAAS LAYER ON COMPOSITIONAL DISORDERING OF ALGAAS/GAAS SUPERLATTICES
(1995-02-01)
TSANG, JS
;
LEE, CP
;
FAN, JC
;
LEE, SH
;
TSAI, KL
Effects of thickness and position of the low-temperature-grown GaAs (LT-GaAs) layer on the compositional disordering of AlGaAs/GaAs superlattice have been studied. Samples with a top LT-GaAs layer or a bottom LT-GaAs layer have been studied with various annealing conditions. It was found that the LT-GaAs layer grown on top of the superlattice is more effective in causing disordering than the LT-GaAs layer grown at the bottom. The amount of disordering increases with the thickness of the LT-GaAs layer. A selective disordering process has been developed using a patterned LT-GaAs cap layer. This disordering technique is very simple and can be easily applied to device fabrication.
EVIDENCE OF ZERO POTENTIAL SPIKE ENERGY IN ALGAAS GAAS HETEROSTRUCTURE EMITTER BIPOLAR-TRANSISTORS
(1993-10-01)
CHEN, HR
;
LEE, CP
;
CHANG, CY
;
TSAI, KL
;
TSANG, JS
The potential spike energy at the emitter junction of AlGaAs/GaAs heterostructure emitter bipolar transistors (HEBT) was directly measured for the first time. Experimental data revealed that emitter thickness as thin as 300 angstrom is thick enough to eliminate potential spike without compositional grading. It is found that the band bending in n-GaAs reduces the potential spike and hence very low offset voltage of 70 mV with high current gain of 150 can be obtained.
FUNDAMENTAL MODE-OPERATION OF HIGH-POWER INGAAS/GAAS/ALGAAS LASER ARRAYS
(1993-05-01)
TSANG, JS
;
LIOU, DC
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TSAI, KL
;
CHEN, HR
;
TSAI, CM
A new ridge waveguide laser array with stable fundamental mode operation has been fabricated. By introducing absorption regions in all the laser stripes except for the central one, the electric field distribution of the laser arrays and the modal gains of the array supermodes are changed, resulting in fundamental mode operation. The threshold current of an array with five elements is typically 40 mA and the maximum output power is higher than 150 mW. The single-lobed far-field pattern centered at 0-degrees with full width at half maximum of 2-degrees is obtained at 1.5 times of the threshold current (I(th)).
HETEROJUNCTION BIPOLAR-TRANSISTORS WITH EMITTER BARRIER LOWERED BY DELTA-DOPING
(1994-08-01)
CHEN, HR
;
HUANG, CH
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CHANG, CY
;
LEE, CP
;
TSAI, KL
An Npn heterojunction bipolar transistor with a Si-delta-doped layer at the emitter-base hetero-interface is demonstrated. The Si delta-doped layer reduces the potential spike at the emitter junction. This design reserves the abruptness of the heterojunction, reduces electron barrier and increases the hole barrier simultaneously. Experimental results show that the HBT's turn-on characteristics are greatly improved while the current gain remains high. The offset voltages as low as 44 mV have been obtained. Very high current gains at very low collector current densities are obtained.
INFLUENCE OF OXYGEN ON THE PERFORMANCE OF GAAS/ALGAAS QUANTUM-WELL INFRARED PHOTODETECTORS
(1994-07-01)
TSAI, KL
;
LEE, CP
;
CHANG, KH
;
CHEN, HR
;
TSANG, JS
The influence of oxygen on the performance of GaAs/AlGaAs quantum well infrared photodetectors (QWIP) has been studied. Photoluminescence and secondary ion mass spectroscopy were used to examine the relationship between the quality of AlGaAs and the oxygen content that were then correlated to the performance of QWIPs. It was found that oxygen is the dominant impurity in the GaAs/AlGaAs superlattice. Because oxygen atoms behave likes electron traps, which effectively reduce the carrier concentration in the material, both of the responsivity and the dark current of QWIP are reduced. The detectivities of QWIPs with lower oxygen concentrations are better than those with higher oxygen concentrations.
INFLUENCE OF THIN PROTECTIVE INAS LAYERS ON THE OPTICAL-QUALITY OF ALGAAS AND QUANTUM-WELLS
(1992-09-15)
TSAI, KL
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CHANG, KH
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LEE, CP
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HUANG, KF
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CHANG, Y
Influence of a thin protective but subsequently evaporated InAs layer on the regrowth of AlGaAs has been studied. It was found tha although most of the InAs could be evaporated by thermal desorption, some would react with Al0.36Ga0.64As to form InAlGaAs. These InAlGaAs islands act as potential wells for carrier recombination and dominate the photoluminescence spectrum. Transmission electron microscopy photographs show that dislocations are formed near the islands. These defects are caused by lattice mismatch between AlGaAs and InAlGaAs. These islands and defects strongly affect the optical quality of surrounding Al0.36Ga0.64As and quantum wells.
INVESTIGATION OF INDIUM DOPING IN INGAAS GAAS ALGAAS GRADED-INDEX SEPARATED CONFINEMENT HETEROSTRUCTURE LASERS
(1993-10-15)
TSANG, JS
;
LEE, CP
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LIU, DC
;
CHEN, HR
;
TSAI, KL
The effect of indium doping in the graded-index regions of the InGaAs/GaAs/AlGaAs graded-index separated confinement heterostructure quantum well laser has been studied. It was found that the threshold current density can be greatly reduced by a proper amount of In doping in the graded AlGaAs region. This result is attributed to an improvement in material quality due to a reduction in group III vacancies. The effect of thermal treatment on laser performance has also been studied. Although high temperature annealing can significantly improve non-In-doped lasers, it has little effect on In-doped lasers.
KINETICS OF COMPOSITIONAL DISORDERING OF ALGAAS/GAAS QUANTUM-WELLS INDUCED BY LAW-TEMPERATURE GROWN GAAS
(1995-05-01)
TSANG, JS
;
LEE, CP
;
LEE, SH
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TSAI, KL
;
CHEN, HR
NOVEL ALGAAS/GAAS HETEROJUNCTION BIPOLAR-TRANSISTORS FABRICATED BY 2-STAGE MOLECULAR-BEAM EPITAXY
(1993-04-01)
CHEN, HR
;
CHANG, CY
;
TSAI, KL
;
TSANG, JS
;
LEE, CP
Two-stage molecular beam epitaxy (MBE) growth was employed to fabricate AlGaAs/GaAs heterojunction bipolar transistors (HBTs) for the first time. Due to the unique base contact layer design, the base can be made very thin without increasing the extrinsic base sheet resistance and the etching of the base contact can be done very easily and very reliably. In addition, the base-collector separation layer design contributed to the reduction of parasitic capacitance. D.C. differential current gains up to 110 and 200 were obtained for 1000 and 500 angstrom base width, respectively.
THE STUDY OF EMITTER THICKNESS EFFECT ON THE HETEROSTRUCTURE EMITTER BIPOLAR-TRANSISTORS
(1993-07-15)
CHEN, HR
;
LEE, CP
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CHANG, CY
;
TSANG, JS
;
TSAI, KL
AlGaAs/GaAs heterostructure emitter bipolar transistors were grown with emitter thicknesses varied from 300 to 900 angstrom and the emitter thickness effects on the current gain and offset voltage were studied. It was found that both the current gain and offset voltage are strongly dependent on the emitter thickness. The current gain decreases with increasing emitter thickness. For an emitter thickness smaller than 500 angstrom, the offset voltage decreases with increasing emitter thickness, but for an emitter thickness larger than 500 angstrom, the offset voltage stays at a nearly constant value. Offset voltage as low as 55 mV was obtained for an emitter thickness of 700 angstrom. This low offset voltage, mostly contributed by the geometric effect, indicates that the base-emitter junction is a homojunction. From the current gain and offset voltage considerations, the optimal emitter thickness was found to be about 300-500 angstrom.
TRANSIENT ANALYSIS OF AN ASYMMETRIC ROTOR-BEARING SYSTEM DURING ACCELERATION
(1992-11-01)
LEE, AC
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KANG, Y
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TSAI, KL
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HSIAO, KM
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交大名義發表
This paper deals with the transient vibration of asymmetric rotor systems during acceleration passing through several critical speeds at which synchronous or super-harmonic resonance occurs. The dynamic equations of the rotor-bearing system are formulated by the finite element model and the resulting dynamic equations are time-varying due to the effects of acceleration and asymmetry. In the formulation, a Timoshenko beam element is employed to simulate the rotating shaft and Eulerian angles are used to describe the orientations of the shaft element and disk. The numerical integration scheme for transient analysis is generated from the finite element model. Numerical examples are presented to illustrate (1) the effects of acceleration on peak amplitude and speed at which the peak occurs as the system passes through critical speeds, (2) the optimal acceleration process, which can be obtained by minimizing the peak response and the period of acceleration, (3) the speed regions where the transient instability exists.
VERTICAL INTEGRATION OF A GAAS/ALGAAS QUANTUM-WELL LASER AND A LONG-WAVELENGTH QUANTUM-WELL INFRARED PHOTODETECTOR
(1994-03-03)
TSANG, JS
;
LEE, CP
;
TSAI, KL
;
CHEN, HR
;
電子工程學系及電子研究所
A short-wavelength (approximately 0.8mum) GaAs/AlGaAs graded-index separate-confinement heterostructure quantum-well laser has been monolithically integrated with a long-wavelength (approximately 8mum) GaAs/AlGaAs multiple-quantum-well infra-red photodetector on a semi-insulating GaAs substrate by molecular beam epitaxy. The vertical integration method is used and the combined structure is a pinin structure. Both the laser and detector exhibit excellent characteristics. At room temperature, the ridge waveguide laser has an extremely low threshold current of 25 mA and a differential quantum efficiency above 65% with a stripe width of 20mum. The quantum-well detector has a peak response at 8mum and a responsivity of 0.7A/W.