Preparation of Zinc Oxide Films by Low-Pressure Chemical Vapor Deposition Method
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Junichi NISHINO, Shigeo OHSHIO, and Kiichiro KAMATA, Department of Chemistry, Nagaoka University of Technology, Nagaoka, Niigata, 940-21, Japan
ABSTRACT ZnO and Al-doped ZnO films prepared using a low-pressure chemical vapor deposition (LP-CVD) method were studied. The films were prepared on fused quartz substrates using bis(2,4-pentanedionato)zinc and tris(2,4-pentanedionato)aluminum which are inexpensive and stable source materials. The highly c-axis oriented ZnO films were grown on the substrates above 500'C. The minimum electrical resistivity of p=6.5Xl0-52m was obtained for the ZnO film, and of p = 3.5X10- 5 Qm was obtained for the ZnO:AI film. I. Introduction Zinc oxide, a semiconducting, photo conducting, piezoelectric, and optical wave guide material', shows a wide range of scientific and technological applications 2' 3 . Also, thin film ZnO is used as a detector of oxidizing and reducing gases in chemical sensors, and as a transparent electrode material in light-emitting diodes and solar cells 4 ' 5 . In particular, the reduction in the basic cost of the cells is the most important object to get for the solar cells6 . Therefore zinc oxide film is highly important as a thin film material. Previously, we reported results on ZnO 7 and ZnO:A18 films prepared by chemical vapor deposition under atmospheric pressure using bis(2,4-pentanedionato)zinc and tris(2,4pentanedionato)aluminum. This report presents the results of the ZnO films prepared by a low-pressure process. 11. Experimental Procedure Zinc Oxide films were prepared using a low-pressure thermal-CVD process. The schematic diagram of the apparatus and a listing of the preparation conditions are shown in Fig. I and Table I, respectively. The N2 carrier gas was introduced into the source-material vaporizer heated at 105'C for Zn(C 5 H 70 2)2 and 60-130'C for AI(C 5 H7 0 2 )3 . A mixture of source material vapor and 02 was ejected from a nozzle of 16 mm diameter forward the fused quartz substrates. The substrates were heated on a substrate susceptor by radio frequency power supply. The major parts of this deposition apparatus were made of stainless steel, and the reaction chamber was made of fused quartz. The whole apparatus was heated by ribbon-type heaters to avoid condensation of the source material. Experimental details for film evaluation are similar to those of our previous works7 ' 8 .
219 Mat. Res. Soc. Symp. Proc. Vol. 363 01995 Materials Research Society
Table
I
Experimental Conditions
N2 flow through Zn(C 5 H7 0 2 )2 N2 flow through AI(C 5 H7 0 2 )3
(F(zn))
100 cm3.min 1
(F(AI))
30
Flow rate of 02
(Fr)
2.0 dm3-min" 1
Substrate temperature
Vaporizing temperature of Zn(C 5 H7 0 2 )2
(Ts)
cm3-min-1
350 - 650
0C
(Tv(Zn))
105
0C
(TV(AI))
60-130
°C
Vaporizing temperature of AI(C
5
H7 0 2 )3
Total pressure Substrates
(P)
20,40 kPa Si(100), fused quartz
Fig. I. Schematic diagram of CVD apparatus.
220
III. Results and Discussions (A) ZnO films Figure 2 shows the map of film structure with total gas pressure and substrat
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