Semiconductor device manufacturing: process – Formation of semiconductive active region on any substrate – Fluid growth from liquid combined with preceding diverse...
Reexamination Certificate
2000-02-04
2001-10-23
Bowers, Charles (Department: 2813)
Semiconductor device manufacturing: process
Formation of semiconductive active region on any substrate
Fluid growth from liquid combined with preceding diverse...
C438S046000, C438S102000, C438S497000, C438S962000, C257S064000, C420S513000, C420S525000, C420S526000, C423S289000, C423S299000
Reexamination Certificate
active
06306736
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for making shaped semiconductor nanocrystals and a resulting product therefrom. More particularly, this invention relates to a process for controlling the shape of Group III-V semiconductor nanocrystals during the formation of same.
2. Description of the Related Art
Semiconductor nanocrystals, such as Group III-V nanocrystals are formed by dissolving a Group III precursor and a Group V precursor in a solvent and then applying heat to the solvent and the precursors therein.. For example, Group III-V semiconductor nanocrystals may be formed by dissolving a dialkyl of the Group III metal and a Group V powder in a trialkyl phosphine solvent at ambient temperature, and then injecting the mixture into a heated (340° C.-360° C.) bath of tri-octyl phosphine oxide (TOPO).
While the just described process is capable of producing Group III-V semiconductor nanocrystals, the results can be somewhat erratic in terms of average particle size and size distribution. While it is not certain why the process is not always reproducible, it is believed that impurities in the technical grade (90% pure) TOPO may be adversely influencing the reaction. However, substitution of pure TOPO for the technical grade TOPO has also been unsatisfactory, particularly when control of the shape of the particle growth is also desired, apparently because the pure TOPO binds too weakly to the growing crystallites and only weakly associates with the Group III metal to act as a growth retardant, resulting in the growth of spheres rather than any other desired shapes. Apparently, the presence of impurities in the technical grade TOPO may result in the erratic success of Group III-V semiconductor nanocrystal growth in technical grade TOPO. The growth of rod-like semiconductor crystals has been reported by W. Z. Wang et al. in “Synthesis and Characterization of MSe (M=Zn, Cd) nanorods by a New Solvothermal Method”, Inorganic Chemistry Communications 1999 Mar, Vol. 2, N3:83-85. However, the rod-shaped crystals are out of the confinement region, i.e., are not of nanocrystal dimensions.
Alivisatos et al. U.S. Pat. No. 5,505,928, by one of us with another, and assigned to the assignee of this invention, and the subject matter of which is hereby incorporated by reference, describes a process for forming Group III-V semiconductor nanocrystals wherein size control is achieved through use of a crystallite growth terminator which controls the size of the growing crystals. Crystallite growth terminators are said to include a nitrogen-containing or a phosphorus-containing polar organic solvent having an unshared pair of electrons. The patent states that this growth terminator can complex with the metal and bind to it, thereby presenting a surface which will prevent further crystal growth.
Examples of suitable nitrogen-containing materials which can serve as such Group III-V growth terminators are said to include nitrogen-containing aromatics or heterocyclics such as pyridine, quinoline, pyrimidine, imidazole and the purines and benzoimidazoles, as well as 2-methylpyridine, 3-ethylpyridine, 4-chloropyridine, collidine, dimethylquinoline, and the like.
Group III-V crystallite growth terminators described in Alivisatos et al. U.S. Pat. No. 5,505,928, which contain phosphorus-containing materials include phosphine, mono-, di-, and tri-(C
1-6
alkyl)phosphine, e.g., PH
2
CH
3,
PH(CH
3
)
2
P(CH
3
)
3
, PH
2
(C
4
H
9
), PH(C
5
H
11
)
2
, and P(C
6
H
13
)
3
; and C
1-6
alkylphosphites such as P—(OCH
3
)
3
, P—(OC
2
H
5
)
3
, and P—(OC
3
H
7
)
3
.
Since Group III-V semiconductor nanocrystals are of interest for use in optical displays, as well as in biological applications, it would be desirable to provide a process for control of shape as well as size growth of such Group Ill-V semiconductor nanocrystals wherein the shape (aspect ratio), as well as the particle size, growth rate, and particle size distribution, can be reproducibly controlled, whereby, for example, spheres or rods of semiconductor nanocrystals of controlled dimensions could be formed in a controllable and repeatable manner.
SUMMARY OF THE INVENTION
In accordance with the invention, a process for the formation of shaped Group III-V semiconductor nanocrystals comprises contacting a solution of the semiconductor nanocrystal precursors with a liquid media comprising a binary surfactant mixture capable of promoting the growth of either spherical semiconductor nanocrystals or rod-like semiconductor nanocrystals, whereby the shape of the semiconductor nanocrystals formed in the binary mixture of surfactants can be controlled by adjusting the ratio of the surfactants in the binary mixture.
REFERENCES:
patent: 5262357 (1993-11-01), Alivisatos et al.
patent: 5474591 (1995-12-01), Wells et al.
patent: 5505928 (1996-04-01), Alivisatos et al.
patent: 5537000 (1996-07-01), Alivisatos et al.
patent: 5751018 (1998-05-01), Alivisatos et al.
Dabbousi, B.O., et al., “(CdSe) ZnS Core-Shell Quantum Dots: Synthesis and Characterization of a Size Series of Highly Luminescent Nanocrystallites”,Journal of Physical Chemistry B, vol. 101, 1997, pp. 9463-9475.
Peng, Xiaogang, et al., “Epitaxial Growth of Highly Luminescent CdSe/CdS Core/Shell Nanocrystals with Photostability and Electronic Accessibility”,Journal of the American Chemical Society, vol. 119, No. 30, pp. 7019-7029.
Bruchez, M., Jr., et al., “Semiconductor Nanocrystals as Fluorescent Biological Labels”,Science, 281, Sep. 25, 1998, pp. 2013-2016.
Han, W., et al., “Synthesis of Gallium Nitride Nanorods Through a Carbon Nanotube-Confined Reaction”,Science, 277, Aug. 29, 1997, pp. 1287-1289.
Huynh, W.U., et al., “CdSe Nanocrystal Rods/Poly(3-hexylthiophene) Composite Photovoltaic Devices”,Advanced Materials, 11, 1999, pp. 923-927.
Kabay, N., et al., “Removal of Metal Pollutants (Cd(II) and Cr (III)) from Phosphoric Acid Solutions by Chelating Resins Containing Phosphonic or Diphosphonic Groups”,Industrial&Engineering Chemistry Research, 37, 1998, pp. 2541-2547.
Kolosky, M., et al., “Determination of Trioctylphosphine Oxide and Its Impurities by Reversed-Phase High-Performance Liquid Chromatography”,Journal of Chromatography, 299, 1984, pp. 436-444.
Lieber, C.M., “One-Dimensional Nanostructures: Chemistry, Physics & Applications”,Solid State Communications, 107, (11), 1998, pp. 607-616.
Murray, C.B., et al., “Synthesis and Characterization of Nearly Monodisperse CdE (E=S, Se, Te) Semiconductor Nanocrystallites”,Journal of the American Chemical Society, 115, 1993, pp. 8706-8715.
Peng, X., et al., “Kinetics of II-VI and III-V Colloidal Semiconductor Nanocrystal Growth: ‘Focusing’ of Size Distributions”,Journal of the American Chemical Society, 120, 1998, pp. 5343-5344.
Routkevitch, D., et al., “Electrochemical Fabrication of CdS Nanowire Arrays in Porous Anodic Aluminum Oxide Templates”,Journal of Physical Chemistry, 100, 1996, pp. 14037-14047.
Schlamp, M.C., et al., “Improved Efficiencies in Light Emitting Diodes Made with CdSe (Cds) Core/Shell Type Nanocrystals and a Semiconducting Polymer”,Journal of Applied Physics, 82, (11), Dec. 1, 1997, pp. 5837-5842.
Wang, W., et al., “Synthesis and Characterization of MSe (M=Zn, Cd) Nanorods by a New Solvothermal Method”,Inorganic Chemistry Communications, 2, 1999, pp. 83-85.
Alivisatos A. Paul
Manna Liberato
Peng Xiaogang
Bowers Charles
Sarkar Asok Kumar
Taylor John P.
The Regents of the University of California
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