Browsing by Author "Guo, XJ"

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Carrier distribution and relaxation-induced defects of InAs/GaAs quantum dots
(2000-11-06)
Wang, JS
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Chen, JF
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Huang, JL
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Wang, PY
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Guo, XJ
The carrier distribution and defects have been investigated in InAs/GaAs quantum dots by cross-sectional transmission electron microscopy (XTEM), capacitance-voltage, and deep level transient spectroscopy. Carrier confinement is found for 1.1- and 2.3-monolayer-(ML)-thick InAs samples. For 2.3 ML sample, XTEM images show the presence of defect-free self-assembled quantum dots. With further increase of the InAs thickness to 3.4 ML, significant carrier depletion caused by the relaxation is observed. In contrast to 1.1 and 2.3 ML samples in which no traps are detected, two broad traps and three discrete traps at 0.54, 0.40, and 0.34 eV are observed in 3.4 ML sample. The traps at 0.54 and 0.34 eV are found to be similar to the traps observed in relaxed In0.2Ga0.8As/GaAs single quantum well structures. By comparing with the XTEM images, the trap at 0.54 eV is identified to be the relaxation-induced dislocation trap in the GaAs layer. (C) 2000 American Institute of Physics. [S0003-6951(00)02245-2].
Effect of substrate orientation on arsenic precipitation in low-temperature-grown GaAs
(2005-09-01)
Lee, WN
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Chen, YF
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Huang, JH
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Guo, XJ
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Kuo, CT
Arsenic precipitation in "superlattice" structures of alternately undoped and [Si] = 3 x 10(18) cm(-3)-doped GaAs grown at 250 degrees C on (100), (311)A, and (311)B GaAs substrates has been studied using transmission electron microscopy. It is found that upon postgrowth annealing at 800 degrees C, As precipitates are nearly confined in the Si-doped regions, forming two-dimensional cluster arrays located approximately at the center of each Si-doped layer. The results also show that the As precipitates in the (311)B substrate are slightly denser and larger than those in the (311)A substrate and both are markedly denser and larger than those in the (100) substrate. This can be attributed to the varying excess arsenic incorporations in differently orientated substrates.
Effects of annealing on magnetic properties of new ferromagnetic semiconductor (In, Al, Mn) As
(2005-10-01)
Chen, YF
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Lee, WN
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Huang, JH
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Chin, TS
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Guo, XJ
The effects of low-temperature (210 degrees C-290 degrees C) annealing on the microstructure, lattice constant, and magnetic properties of (In0.52Al0.48)(0.91)Mn0.09As grown by low-temperature molecular-beam epitaxy were studied. The results show that low-temperature annealing has little influence on the crystalline structure and interface quality Of (In0.52Al0.48)(0.91)Mn0.09As epilayer. In contrast, both the lattice constant and Curie temperature of (In0.52Al0.48)(0.91)Mn0.09As are found to be strongly dependent on the annealing temperature. The lattice constant linearly decreases with increasing annealing temperature; while the Curie temperature increases with increasing annealing temperature up to 250 degrees C, and then abruptly decreases upon further annealed at 270 degrees C and 290 degrees C.
Effects of doping type and concentration on precipitation of nanometer arsenic clusters in low-temperature-grown GaAs
(2005-11-01)
Lee, WN
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Chen, YF
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Huang, JH
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Guo, XJ
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Kuo, CT
In this study, the effects of doping type and concentration on arsenic precipitation in low-temperature-grown GaAs upon postgrowth annealing at 600, 700. and 800 degrees C were investigated. Three undoped/Si-doped/undoped (i-n-i) regions and three undoped/Be-doped/ undoped (i-p-i) regions were grown by low-temperature Molecular beam epitaxy, The results show that arsenic precipitation is dependent on doping type and doping concentration. Arsenic depletion was observed in all Be-doped layers for all annealing temperatures. However, a "dual" arsenic precipitation behavior was observed in Si-doped layers: As accumulates in [Si]=2 X 10(18) cm(-3) doped layers, while it depletes in [Si]=2 X 10(16) and 2 X 10(17) cm(-3) doped layers, We attribute this "dual" As precipitation phenomenon in Si-doped layers to the different depletion depths. (c) 2005 American Vacuum Society.
(In0.52Al0.48)(1-x)MnxAs muted magnetic semiconductor grown on InP substrates
(2006-01-11)
Lee, WN
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Chen, YF
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Huang, JH
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Guo, XJ
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Kuo, CT
A series of diluted magnetic semiconductors, (In0.52Al0.48)(1-x)MnxAs (0 < x <= 0. 11), was successfully grown on InP substrate by low-temperature molecular beam epitaxy. Our results indicate that (In0.52Al0.48)(1-x)MnxAs exhibits interesting magnetic behaviours at 5 K: it shows paramagnetic-like behaviour when x <= 0.05 and ferromagnetic behaviour when x >= 0.06.
MBE growth and structural and magnetic properties of (In1-gamma Al gamma)(1-x)MnxAs-diluted magnetic semiconductors
(2006-04-01)
Lee, WN
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Chen, YF
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Huang, JH
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Guo, XJ
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Kuo, CT
A series of quaternary-diluted magnetic semiconductors, (In1-y,Al-y)(1-x)MnxAs, have been successfully grown on InP substrates by low-temperature molecular beam epitaxy. The (ln(0.52)Al(0.48))(1-x)MnxAs with x <= 0.11 were grown on a nearly lattice-matched In0.52Al0.48As buffer, while the (In1-y,Al-y)(1-x)MnxAs with a higher Mn content of 0.11 < x <= 0.18 were grown on a graded 3-layer In,-,,Al-y 'As buffer structure. The results of transmission electron microscopy and double-crystal X-ray diffraction reveal that all (In1-yAly)(1-x),Mn,As epilayers are single crystal with zincblende structure, and the lattice constant increases with increasing the Mn content. The magnetic measurements show that the (In1-y,Al-y)(1-x)MnxAs semiconductors exhibit a paramagnetic-like state for x <= 0.05 while a ferromagnetic state for x >= 0.05, and the Curie temperature of ferromagnetic (In1-yAly)(1-x) MnxAs increases with increasing Mn content. (c) 2006 Elsevier B.V. All rights reserved.
Strain relaxation in In0.2Ga0.8As/GaAs quantum-well structures by x-ray diffraction and photoluminescence
(2000-02-01)
Chen, JF
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Wang, PY
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Wang, JS
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Chen, NC
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Guo, XJ
The onset of strain relaxation in In0.2Ga0.8As/GaAs quantum-well structures is investigated. X-ray diffraction shows that when the InGaAs thickness increases beyond its critical thickness, another peak on the right shoulder of the GaAs peak appears, indicating that the top GaAs layer is being compressed in the growth direction by the relaxation of the InGaAs layer. Energy shifts of 44 and 49 meV are observed, respectively, from the strains of the InGaAs and GaAs top layers when increasing the InGaAs thickness from 300 and 1000 Angstrom. These energy shifts are in agreement with theory calculated based on the relaxation process observed in x-ray diffraction, providing evidence that the relaxation occurs from near the bottom InGaAs/GaAs interface while the top interface still remains strained. This result is further corroborated by the images of cross-sectional transmission electron micrographs which show that most of the misfit dislocations are confined near the bottom interface. (C) 2000 American Institute of Physics. [S0021-8979(00)07303-5].
The microstructure of As precipitates in Si delta-doped GaAs grown by low-temperature molecular beam epitaxy
(1997-11-01)
Hsieh, LZ
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Huang, JH
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Su, ZA
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Guo, XJ
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Shih, HC
The structure relationship of the As precipitates found in post-annealed Si delta-doped GaAs layers grown by low-temperature molecular beam epitaxy is elucidated by transmission electron microscopy (TEM). There are six extra spots around the diffraction pattern of GaAs for a sample annealed at 700 degrees C. The As precipitates and GaAs matrix are found to be semicoherent with the hexagonal [-1-21](As) parallel to the cubic [110](GaAs). Because of the different lattice constants and Bravias lattices between GaAs and As precipitates, these extra spots are formed by double-diffraction effects. The high-resolution TEM images show two types of Moire fringes. One is the parallel Moire pattern and the other is the rotation Moire pattern. The relative positions of the extra spots in the diffraction pattern correspond to the orientation and spacing of Moire fringes.
The microstructure of As precipitates in Si delta-doped GaAs grown by low-temperature molecular beam epitaxy
(1997-11-01)
Hsieh, LZ
;
Huang, JH
;
Su, ZA
;
Guo, XJ
;
Shih, HC
The structure relationship of the As precipitates found in post-annealed Si delta-doped GaAs layers grown by low-temperature molecular beam epitaxy is elucidated by transmission electron microscopy (TEM). There are six extra spots around the diffraction pattern of GaAs for a sample annealed at 700 degrees C. The As precipitates and GaAs matrix are found to be semicoherent with the hexagonal [-1-21](As) parallel to the cubic [110](GaAs). Because of the different lattice constants and Bravias lattices between GaAs and As precipitates, these extra spots are formed by double-diffraction effects. The high-resolution TEM images show two types of Moire fringes. One is the parallel Moire pattern and the other is the rotation Moire pattern. The relative positions of the extra spots in the diffraction pattern correspond to the orientation and spacing of Moire fringes.