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MOCVD of the Blue Electro-luminescent Phosphor CaGa2 S4:Ce from a Liquid Reagent Delivery System

Published online by Cambridge University Press:  10 February 2011

T.S. Moss ,
R.C. Dye ,
D.C. Smith ,
J.A. Samuels ,
M.J. DelaRosa  and
C.F. Schaus
T.S. Moss
Affiliation:
Los Alamos National Laboratory, M.S. E549, Los Alamos, NM 87445
R.C. Dye
Affiliation:
Los Alamos National Laboratory, M.S. E549, Los Alamos, NM 87445
D.C. Smith
Affiliation:
Los Alamos National Laboratory, M.S. E549, Los Alamos, NM 87445
J.A. Samuels
Affiliation:
Los Alamos National Laboratory, M.S. E549, Los Alamos, NM 87445
M.J. DelaRosa
Affiliation:
Planar Systems, Inc., Beaverton, OR
C.F. Schaus
Affiliation:
Planar Systems, Inc., Beaverton, OR
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Abstract

The deposition of CaS, Ga2S3, and CaGa2S4:Ce has been accomplished by MOCVD using Ca(tmhd)2, Ga(tmhd)3, and Ce(tmhd)4, with bubblers and with a liquid delivery system to control the flows. Samples were primarily characterized using x-ray fluorescence and electroluminescence measurements of the color and brightness. Deposition using the bubblers showed a definitive relationship between the Ga(tmhd)3 bubbler temperature and the Ga XRF counts. The Ca conversion shows a tenuous relationship with the Ca(tmhd)2 bubbler temperature, but the scatter of the data makes determining a correlation impractical. Use of the liquid delivery system is preferred to the bubblers because it delivered a reliable reagent flow without the same problems of degradation of the reagent over time. Analysis shows the CaS deposition is mass transport limited, while the Ga2S3 is limited by the deposition kinetics. However, application of these mechanisms to the CaGa2S4:Ce deposition system reveals that the CaGa2S4:Ce is independent of its components. Further, the deposition of CaGa2S4:Ce is found to be Ca rich under conditions which leads to low Ga/Ca ratios in the deposited film. This indicates that the conversion of Ca from Ca(tmhd)2 was catalyzed by the slight presence of Ga in the form of CaGa2S4:Ce or Ga2S3 on the surface. The Ca is thought to be deposited as CaS:Ce since there is a shift in the EL color towards green under low Ga/Ca ratios. The Ca conversion is also found to approach values predicted by the CaS deposition mechanism under conditions which lead to high Ga/Ca ratios, implying that excess Ga2S3 is needed for the deposition of CaGa2S4:Ce without any CaS:Ce inclusions.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 415: Symposium BB – Metal-Organic Chemical Vapor Deposition of Electronic Ceramics II , 1995 , 21
Copyright
Copyright © Materials Research Society 1996

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References

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