Thin A-SiO x H y Alloy Films Showing Visible Luminescence Prepared by DC-Magnetron Sputtering with Water Vapor as Oxygen
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THIN A-SiOxHy ALLOY FILMS SHOWING VISIBLE LUMINESCENCE PREPARED BY DC-MAGNETRON SPUTTERING WITH WATER VAPOR AS OXYGEN SOURCE M. ZACHARIAS*, B. GARKE*, A. PANCKOW*, H. FREISTEDI, AND T. DRUSEDAU* ** * Inst. Exper. Physik, Tech. Univ. "Otto von Guericke", 0-3010 Magdeburg, Germany ** Feodor Lynen-Fellow of the Alexander von Humboldt - Fundation, present address:
Harvard University, Division of Applied Sciences, Cambridge, MA 02138 ABSTRACT Thin films of non stochiometric hydrogenated amorphous silicon oxide (a-SiOxHy.) with x=0.09... 1.14, y=0.06...0.20 were prepared by dc-magnetron sputtering from a crystalline silicon target within an argon-hydrogen-water vapor atmosphere. The film properties were investigated by infrared and optical spectroscopy, Rutherford backscattering spectroscopy (RBS) and elastic recoil detection (ERD), luminescence and activated conductivity. Absorption bands related to either silicon-hydrogen or silicon-oxygen vibration modes were 1 observed at 650, 800, 870 and 1000cm- . Above a water pressure of 0.06Pa, the oxygen content saturates at about 50 at%. The static refractive index n-*, the optical Tauc gap ET and the logarithmic dark conductivity at room temperature show a linear dependence on the films' oxygen content. Films prepared under certain conditions show visible photoluminescence. INTRODUCTION Amorphous silicon oxide is a widely used insulating thin film material. Alloying of hydrogenated amorphous silicon with oxygen results in a ternary system, which will be referred to in the following as a-SiOxHy. There are previous reports on the preparation of this material by magnetron sputtering from a SiO 2 target or from a Si target within a sputtering atmosphere containing either 02 or H2 0 11-31. The recent observation that substitutes from siloxene (Si 6 0 3H6 ) show a strong visible photoluminescence [4] very similar to porous silicon prepared by anodic etching [5, 61 makes it worthwhile to re-investigate the preparation and the physical properties of a-SiOxHy. The preparation of such a compound as a thin film might be of great scientific interest. SAMPLE PREPARATION AND FILM PROPERTIES A detailed description of the sputtering apparatus and thin film characterization methods Table I: Variation of process parameters and resulting optical properties of the a-SiOxHy films investigated in the present work. Symbols represent each set in the figs.
Set No
Variation of
Refractive Index n
Tauc-gap ET [eV]
X [ at%] 47-42
1
PH20 0.1-0.5 Pa
1.6-2.1
2
PH20 = .015-.075 Pa PH2 = 0.1-0.6 Pa PH20 = 0.01-0.04 Pa TS = 40-140 °C PH20 = 0.01-0.1 Pa
2.8- 1.8
1.59-2.39
19-45
2.2-2.3
1.98-2.01
27-29
2.5-2.0
1.75-2.18
24-40
19-2.5
2.08-193
34-22
3 4 5 6
1.9_-2.5 2.6- 1.8
_.081.93 _
1.87-2.61
_34 _
25-46
Mat. Res. Soc. Symp. Proc. Vol. 297. c1993 Materials Research Society
Symbol open circle open square open diamond open triangle closed circle closed diamond
754
2.0
•
1.5
Msq
z 0
1.0
0
0.5 0• U,
0.0 600
700
800 900 WAVENUMBER
1000 k [cm" 1]
1100
1200
Fig. 1: IR ab
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