Coating processes – Coating by vapor – gas – or smoke – Mixture of vapors or gases utilized
Patent
1996-06-12
1998-06-30
King, Roy V.
Coating processes
Coating by vapor, gas, or smoke
Mixture of vapors or gases utilized
4272551, 4272481, 427 69, 427 66, 427 64, 117108, 438603, C23C 1424, B05D 506
Patent
active
057730857
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a ternary compound thin film and a method of manufacturing the same, and more particularly relates to a crystal growing technique for forming a thin film of a ternary compound semiconductor material such as SrGa.sub.2 S.sub.4 and a ternary compound phosphor thin film having a basic substance of said ternary compound semiconductor material by means of the vacuum vapor deposition method or molecular beam epitaxial method (MBE method).
TECHNICAL BACKGROUND
SrGa.sub.2 S.sub.4 is one of the ternary compound semi-conductor material and has a wide band-gap up to 4.4 eV, so that this material may be advantageously used as a basic material of phosphors emitting radiation in a short wavelength region. T. E. Peters et al have reported in "Journal of Electrochemical Society: SOLID STATE SCIENCE AND TECHNOLOGY", 119 (1972), pp.230-236 that a cerium doped SrGa.sub.2 S.sub.4 (SrGa.sub.2 S.sub.4 :Ce) powder phosphor emits blue luminescent light having good color purity. However, it is practically difficult to obtain an AC driven thin film electroluminescent device having an ideal stoichiometric ratio (Sr:Ga:S=1:2:4) from this SrGa.sub.2 S.sub.4 material. When the ideal stoichiometric ratio is not attained, the color purity is deteriorated and the emission efficiency is decreased.
In order to solve the above mentioned problem, Planar Systems Inc., U.S.A. has proposed a thin film manufacturing method, in which a strontium thiogallate SrGa.sub.2 S.sub.4 thin film is formed by a sputtering method using a target having an excess amount of Ga.sub.2 S.sub.3 by 3-5% for supplementing elements which will be lost during a film forming process as well as a high temperature annealing process (Japanese Patent Application Laid-open Publication Kokai Hei 5-65478). However, a thin film formed by the sputtering method is amorphous (non-crystal), and thus it is necessary to perform a crystallization process after forming a thin film by means of a high temperature annealing. Therefore, even by this method it is difficult to obtain a phosphor thin film having a high quality of crystallinity. For instance, when the above phosphor is applied to the AC driven thin film electroluminescent device emitting blue light, there were drawbacks that the light emission efficiency is low and the brightness is also low.
A vacuum vapor deposition method in an ultra high vacuum and a molecular beam epitaxial method have been known as a method of manufacturing a thin film having a high degree of crystallinity. In these methods, there are used evaporation sources for particular elements constituting a compound semiconductor material. For instance, when a SrGa.sub.2 S.sub.4 ternary compound semiconductor thin film is to be formed, strontium metal Sr, gallium metal Ga and sulfur element S are prepared as evaporation sources.
When the SrGa.sub.2 S.sub.4 ternary compound semiconductor thin film is formed by using particular element evaporation sources, a binding energy between sulfur element S and strontium metal Sr and a binding energy between sulfur element S and gallium metal Ga differ greatly from each other, so that it is difficult to form a thin film having a desired stoichiometric ratio. Further, sulfur element S has a high vapor pressure at a low temperature, so that it is difficult to control a supply amount of sulfur, and further a vacuum system of the film forming apparatus is stained with sulfur.
The present invention has for its object to provide a method of manufacturing, on a substrate, a ternary compound thin film having a good crystal property and having a desired stoichiometric ratio, while the above mentioned problems could be removed.
It is another object of the invention to provide a ternary compound phosphor thin film emitting blue light with a high emission efficiency.
It is still another object of the invention to provide a blue light emitting electroluminescent device which can emit blue light required for a color display.
DISCLOSURE OF THE INVENTION
In order to attain the abov
REFERENCES:
patent: 4770950 (1988-09-01), Ohnishi
patent: 5505986 (1996-04-01), Velthaus et al.
patent: 5554449 (1996-09-01), Tonomura et al.
T.E. Peters et al., "Luminescence and Structural Properties of Thiogallate Phosphors Ce.sup.+3 and EU.sup.+2 -Activated Phosphors. Part I", J. Electrochem. Soc.: Solid-State Science and Technology, Feb. 1972, pp. 230-236.
Inoue Yoji
Kobayashi Kikuo
Okamoto Shinji
Tanaka Katsu
King Roy V.
Nippon Hoso Kyokai
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