Browsing by Author "LIU, DG"

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A NOVEL TECHNIQUE FOR LOW-THRESHOLD AND HIGH-POWER INGAAS/GAAS STRAINED-LAYER 0.98-MU-M BURIED HETEROSTRUCTURE LASER FABRICATION
(1992-02-01)
LIOU, DC
;
CHIANG, WH
;
LEE, CP
;
CHANG, KH
;
LIU, DG
A novel fabrication technique has been developed for InGaAs/GaAs strained-layer buried heterostructure lasers. Dielectric masks and Zn diffusion are not required in this technique. This novel fabrication process is much easier than the conventional approach and yields excellent laser results. A low threshold of 3 mA and high-power operation for lasing wavelength of 9800 +/- 20 angstrom have been achieved with graded index separate confinement heterostructure devices using this novel technique.
ANALYSIS OF SEVERAL HIGH-ELECTRON-MOBILITY-TRANSISTOR STRUCTURES BY A SELF-CONSISTENT METHOD
(1991-03-01)
LIU, DG
;
CHIN, TC
;
LEE, CP
;
HWANG, HL
;
電控工程研究所
Three HEMT structures, the single heterostructure HEMT (SH-HEMT), the quantum well HEMT (QW-HEMT) and the delta-doped HEMT (delta-HEMT) were analyzed by solving the Schroedinger equation and Poisson equation self-consistently. The potential and the carrier distributions as well as the charge controlled by gate bias were calculated for different structural parameters. Parallel conduction in AlGaAs, which is severe for SH-HEMTs, is greatly reduced in QW-HEMT and delta-HEMT structures. The effect of layer parameters such as spacer layer thickness and quantum-well width on device performance has been studied. SH-HEMT and QW-HEMT have been fabricated for the confirmation of our analysis.
BEHAVIOR OF THE 1ST LAYER GROWTH IN GAAS MOLECULAR-BEAM EPITAXY
(1990-10-01)
LIU, DG
;
LEE, CP
;
CHANG, KH
;
WU, JS
;
LIOU, DC
CHARACTERIZATION OF IMPROVED ALGAAS/GAAS RESONANT TUNNELING HETEROSTRUCTURE BIPOLAR-TRANSISTORS
(1991-02-01)
WU, JS
;
CHANG, CY
;
LEE, CP
;
CHANG, KH
;
LIU, DG
We report on the fabrication of AlGaAs/GaAs resonant tunneling heterostructure bipolar transistors (RTHBT's). The devices exhibit a current peak in the transfer characteristics, with peak-to-valley current ratios of 1.7 and 9 at 300 K and 77 K, respectively. The common-emitter small signal current gains at 300 K and 77 K reach 40 and 28, respectively. They are the best results to date for AlGaAs/GaAs resonant tunneling transistors. Because the double barriers are placed in the emitter and far from the emitter-base interface, and the heterostructure emitter suppresses the hole injection from the base to the emitter, the occurrence of the negative differential resistance (NDR) in the device characteristics is governed by the emitter current but not by the base current. The operation mechanism of the NDR behavior in the common-emitter output characteristics is discussed.
DELTA-DOPED QUANTUM-WELL STRUCTURES GROWN BY MOLECULAR-BEAM EPITAXY
(1990-10-29)
LIU, DG
;
LEE, CP
;
CHANG, KH
;
WU, JS
;
LIOU, DC
DIRECT OBSERVATION OF SI DELTA-DOPED GAAS BY TRANSMISSION ELECTRON-MICROSCOPY
(1992-05-25)
LIU, DG
;
FAN, JC
;
LEE, CP
;
TSAI, CM
;
CHANG, KH
Direct observation of the Si delta-doped layer in GaAs has been achieved by high resolution transmission electron microscopy. Samples with different Si doses, from half a monolayer to two monolayers, were studied. The observed spreading of the delta-doped layer showed that Si atoms are largely confined in five monolayers at most (in the highest dose case), indicating excellent confinements of dopants in GaAs. From the images, the Si atoms were uniformly distributed in the doped layer, no cluster formation was observed. For delta-doped GaAs grown at low temperature (480-degrees-C), stacking faults originated from the doped layers were observed. These faults were thought to be caused by the large unrelaxed strain in the low-temperature grown GaAs.
ELECTRICAL CHARACTERISTICS OF DOUBLE-BARRIER RESONANT TUNNELING STRUCTURES WITH DIFFERENT ELECTRODE DOPING CONCENTRATIONS
(1991-04-01)
WU, JS
;
CHANG, CY
;
LEE, CP
;
CHANG, KH
;
LIU, DG
The electrical characteristics of AlGaAs/GaAs double-barrier resonant tunneling structures with various electrode doping concentrations have been studied. It was found that the peak current and the valley current are not sensitive to the change in the doping level of the electrodes. The peak-current voltage and the valley-current voltage, however, increase when the electrode doping level is lowered. These behaviors are explained using the band-bending effect in the electrodes. For devices with lightly doped or undoped electrodes, the quantum size effect in the accumulation layer due to the strong band bending causes additional kinks in the current-voltage characteristics. They are attributed to the resonant tunneling of electrons from the quantized levels in the accumulation layer. The quantum effect also accounts for the improved negative differential resistance behavior.
FRANZ-KELDYSH OSCILLATIONS OF DELTA-DOPED GAAS
(1992-08-01)
HSU, TM
;
TIEN, YC
;
LU, NH
;
TSAI, SP
;
LIU, DG
Si-delta-doped GaAs (N2D almost-equal-to 10(11) cm-2) samples grown by molecular-beam epitaxy are investigated by using photoreflectance spectroscopy. The oscillations observed above the GaAs fundamental band gap are attributed to the Franz-Keldysh effect in the region between the delta-doped layer and the crystal surface. This ascription is confirmed by detailed studies through varying the cap thickness (250-2500 angstrom), temperature (10-450 K), and laser pump power (0.05-7 mW/cm2). The surface potential deduced from the Franz-Keldysh oscillations is found to be temperature and laser pump power dependent, which is explained by taking the surface photovoltaic effect into account. The surface Fermi level has been measured by this method and is found to have the value 0.73+/-0.02 V.
HIGH-QUALITY ALGAAS LAYERS GROWN BY MOLECULAR-BEAM EPITAXY AT LOW-TEMPERATURES
(1992-03-01)
CHANG, KH
;
WU, JS
;
LIU, DG
;
LIOU, DC
;
LEE, CP
Low-temperature (approximately 600-degrees-C) molecular beam epitaxy (MBE) growth of AlGaAs has been studied. It was found that the quality of AlGaAs grown at low temperatures can be as good as that grown at high temperatures ( > 700-degrees-C) if the source materials and the growth chamber are very clean. The threshold currents of Al0.6Ga0.4As/Al0.15Ga0.85As/Al0.6Ga0.4As double heterostructure (DH) lasers grown at low temperatures and high temperatures are almost the same. The material quality can be further improved with a proper amount of indium doping. Photoluminescence (PL) linewidths of 3.1 meV and 1.7 meV have been measured for In-doped Al0.42Ga0.58As and Al0.18Ga0.82As at 4 K, respectively. They are the narrowest linewidths for the MBE-grown AlGaAs with comparable Al contents at any growth temperature. With a proper amount of In doping, double-barrier resonant tunnelling diodes have also shown improved peak-to-valley current ratios.
IMPROVED ALGAAS/GAAS DOUBLE-BARRIER RESONANT TUNNELING STRUCTURES USING 2-DIMENSIONAL SOURCE ELECTRONS
(1991-01-15)
WU, JS
;
LEE, CP
;
CHANG, CY
;
CHANG, KH
;
LIU, DG
We report the enhancement of peak-to-valley current ratios (PVCRs) of double-barrier resonant tunneling structures (DBRTSs) based on the AlGaAs/GaAs material system. The PVCRs as high as 25.4 and 18 have been obtained at 77 K for superlattice and alloy barrier structures with 0.2-mu-m undoped electrodes, respectively. These are the largest PVCRs to date for AlGaAs/GaAs DBRTSs. The large band bending across the undoped electrodes causes size quantization of the accumulation layer, resulting in better resonant tunneling characteristics.
INFLUENCE OF INDIUM DOPING ON ALGAAS LAYERS GROWN BY MOLECULAR-BEAM EPITAXY
(1990-10-15)
CHANG, KH
;
LEE, CP
;
WU, JS
;
LIU, DG
;
LIOU, DC
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
;
LEE, CP
;
HUANG, KF
;
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.
INTRINSIC AND EXTRINSIC EFFECTS ON PERFORMANCE LIMITATION OF ALGAAS/GAAS DOUBLE-BARRIER RESONANT TUNNELING STRUCTURES
(1992-05-01)
WU, JS
;
LEE, CP
;
CHANG, CY
;
CHANG, KH
;
LIU, DG
The performance limitations of negative differential resistance (NDR) in AlGaAs/GaAs double-barrier resonant tunneling structures (DBRTSs) have been investigated by varying the barrier thickness and quantum well (QW) width, and by doping In into the barrier layers. For devices with thick barriers (greater-than-or-equal-to 70 angstrom), the scattering in the material is believed to cause the saturation of the peak-to-valley current ratio (PVCR). The dependence of PVCR on the well width, however, is found to be, to the first-order, not related to the scattering mechanisms or other material properties. It is rather an inherent property of the tunneling process under different conditions. On the other hand, it was found that a proper amount of In doping into the barrier layers can increase the PVCR, because of the lower defect concentration, resulting in lower scattering rate in the active region.
INVESTIGATION OF INDIUM DOPING AND INCORPORATION IN ALGAAS/GAAS DOUBLE-BARRIER RESONANT TUNNELING STRUCTURES
(1991-02-28)
WU, JS
;
CHANG, KH
;
LEE, CP
;
CHANG, CY
;
LIU, DG
In doping and incorporation in the barrier layers of AlGaAs/GaAs double-barrier resonant tunnelling structures (DBRTSs) have been studied. It was found that the peak-to-valley current ratio (PVCR) can be improved by the proper amount of In doping. This is attributed to the improvement in the quality of the AlGaAs barrier layers due to the high surface migration rate of In atoms that reduces group III vacancies. Also pseudomorphic In(x)(Al0.5Ga0.5)(1-x)As/GaAs (x = 0.12) strained-layer DBRTSs have been fabricated by incorporating a sufficient amount of In into the AlGaAs barrier layers. PVCRs as high as 27.5 at 77 K have been obtained. This is the first realisation of such DBRTSs with lattice-mismatched quaternary barrier layers.
PERIODIC FLUX INTERRUPTION AND SUSTAINED TWO-DIMENSIONAL GROWTH FOR MOLECULAR-BEAM EPITAXY
(1989-11-23)
LEE, CP
;
CHANG, KH
;
LIU, DG
;
WU, JS
;
交大名義發表
PHOTOREFLECTION STUDY ON THE SURFACE ELECTRIC-FIELD OF DELTA-DOPED GAAS GROWN BY MOLECULAR-BEAM EPITAXY
(1992-08-15)
LIU, DG
;
CHANG, KH
;
LEE, CP
;
HSU, TM
;
TIEN, YC
Photoreflectance spectroscopy has been used to study the surface electric-field strength and the surface potential of delta-doped GaAs. Franz-Keldysh oscillations in the reflectance spectra were clearly observed and the oscillation periods were used to calculate the internal electric fields of the delta-doped samples. Based on the measured results and the self-consistent calculation, a surface potential of 0.6 eV is obtained.
PRECISE DETERMINATION OF ALUMINUM CONTENT IN ALGAAS
(1991-11-01)
CHANG, KH
;
LEE, CP
;
WU, JS
;
LIU, DG
;
LIOU, DC
The Al composition of AlGaAs has been determined by four methods: high-resolution transmission electron microscopy (HRTEM), reflection high-energy electron diffraction (RHEED), photoluminescence (PL), and double-crystal x-ray diffraction (DCXRD). HRTEM is direct and the most accurate method because it does not involve any formula or extrapolation. Using the result obtained from HRTEM as a standard, we have calibrated the results from other methods. RHEED intensity oscillation is found to be accurate and reliable, if the growth conditions are correctly chosen. Comparing the PL results with those determined from HRTEM and RHEED, we suggest three formulas to determine the Al contents at different temperatures. We also proposed a polynomial to determine the Al concentration using the DCXRD measurement.
QUANTUM EFFECT IN THE ACCUMULATION LAYER ON FIELD-INDUCED PHOTOLUMINESCENCE OF DOUBLE-BARRIER RESONANT TUNNELING STRUCTURES
(1991-07-01)
WU, JS
;
CHANG, KH
;
LEE, CP
;
CHANG, CY
;
LIU, DG
The photoluminescence (PL) of double-barrier resonant tunneling structures (DBRTSs) with undoped electrodes under bias has been studied. The strong band bending across the cathode causes the quantum size effect in the accumulation layer. The resonant tunneling of electrons from the first excited quantum level in the accumulation layer produces a kink in the current-voltage characteristic. It is found that the PL intensity from the quantum well (QW) as a function of bias sharply peaks at the voltage corresponding to the kink. This provides evidence of the interaction between the first excited quantum state in the accumulation layer and the resonant state in the QW.
REPETITION OF NEGATIVE DIFFERENTIAL RESISTANCE IN VERTICALLY INTEGRATED DOUBLE-BARRIER RESONANT TUNNELING STRUCTURES
(1990-05-01)
WU, JS
;
LEE, CP
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CHANG, CY
;
CHANG, KH
;
LIU, DG
RESONANT TUNNELING OF ELECTRONS FROM QUANTIZED LEVELS IN THE ACCUMULATION LAYER OF DOUBLE-BARRIER HETEROSTRUCTURES
(1990-11-26)
WU, JS
;
CHANG, CY
;
LEE, CP
;
CHANG, KH
;
LIU, DG