Browsing by Author "Su, ZA"

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Arsenic precipitate accumulation in alternately Si/Be delta-doped GaAs grown by low-temperature molecular beam epitaxy
(1998-03-15)
Hsieh, LZ
;
Huang, JH
;
Su, ZA
;
Wu, MC
;
電子物理學系
The precipitation of arsenic in alternately [Si]=1.0 x 10(13) cm(-2) and [Be]=1.0 x 10(14) cm(-2) delta-doped GaAs grown at low temperature by molecular beam epitaxy has been studied using transmission electron microscopy. Following annealing at 600, 700 and 800 degrees C, As precipitates were found to form preferentially not only on planes of Si but also on planes of Be. The as-grown and annealed samples were also characterized using secondary ion mass spectroscopy, and the results revealed that the interdiffusion of Si and Be dopants due to annealing was discernible. This is the first observation of As precipitate accumulation on Be delta-doped planes in low-temperature grown GaAs.
Formation of two-dimensional arsenic precipitation in superlattice structures of alternately undoped and heavily Be doped GaAs with varying periods grown by low-temperature molecular beam epitaxy
(1998-05-01)
Su, ZA
;
Huang, JH
;
Lee, WI
;
電子物理學系
;
Department of Electrophysics
As precipitates in superlattice structures of alternately undoped and [Be] = 2.4 x 10(20) cm(-3) doped GaAs with varying periods grown by molecular beam epitaxy at low substrate temperatures were studied by transmission electron microscopy. Never arsenic precipitate microstructures were observed in annealed samples, including preferential accumulation of precipitates inside the Be-doped GaAs but near each interface of Be-doped GaAs and the following grown undoped GaAs. The confinement reaches the extreme for samples annealed at 800 degrees C, where the precipitates appear as dot arrays along such interfaces and leave other areas almost free of precipitates. The incorporation of substitutional Be accepters is believed to cause a smaller lattice constant in the heavily Be-doped regions than in the undoped regions. A strain-induced mechanism was proposed to account for the preferential segregation of As clusters, though the underlying mechanism is not fully clear. (C) 1998 Elsevier Science B.V. All rights reserved.
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.
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.
Two-dimensional arsenic precipitation in superlattice structures of alternately undoped and heavily Be-doped GaAs grown by low-temperature molecular beam epitaxy
(1998-04-20)
Su, ZA
;
Huang, JH
;
Hsieh, LZ
;
Lee, WI
;
電子物理學系
The precipitation of arsenic in superlattice structures of alternately undoped and [Be]=2.4 x 10(19) cm(-3) doped GaAs grown at low temperatures has been studied using transmission electron microscopy. Novel precipitate microstructures were observed in annealed samples, including preferential accumulation of precipitates toward each interface of Be-doped GaAs and the following grown undoped GaAs. Specifically, after 800 degrees C annealing, the precipitates are totally confined in Be-doped regions, forming mio-dimensional dot arrays near the aforementioned interfaces. Data are also presented to show that the heavily Be-doped GaAs has a smaller lattice constant than the undoped GaAs. A strain-induced mechanism was proposed to account for the segregation of As clusters. (C) 1998 American Institute of Physics.