Thin Films of GeC Deposited Using a Unique Hollow Cathode Sputtering Technique
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0910-A07-03
Thin Films of GeC Deposited Using a Unique Hollow Cathode Sputtering Technique James L. Huguenin-Love1, Rodney J. Soukup1, Natale J. Ianno1, Jason S. Schrader1, and Vikram L. Dalal2 1 Department of Electrical Engineering, University of Nebraska-Lincoln, 209N WSEC, Lincoln, NE, 68588-0511 2 Iowa State University, Ames, IA, 50011
ABSTRACT Experimental results on thin films of the new material GexC1-x, deposited by a unique dual plasma hollow cathode sputtering technique are presented here. The (Ge, C) system is extremely promising since the addition of C to Ge has reduced the lattice dimensions enough to allow a lattice match to silicon, while increasing the bandgap close to that of c-Si. The sputtering is accomplished by igniting a dc plasma of the Ar and H2 gases which are fed through Ge and C nozzles, cylindrical tubes 30 mm in length with an outside diameter of 8 mm and an inside diameter of 3 mm. The basic material, optical, and structural properties were analyzed. Film characterization was performed using Fourier transform infra-red spectroscopy (FTIR), X-ray diffraction (XRD), and spectroscopic ellipsometry. The film properties from a variety of deposition conditions are discussed. The measurements made indicate that the films can be grown so that the C enters the material at lattice sites. In addition, the GexC1-x films absorb photons much more efficiently than either c-Si or c-Ge. Initial results on films which include Al as an added impurity are presented. INTRODUCTION The purpose of this research is to experimentally explore thin films of the new material GexC1-x deposited by a unique dual plasma hollow cathode sputtering technique. This technique for the deposition of GeC has been discussed1,2, the continuation of this study presented here includes deposition onto HF etched Si and the inclusion of Al in the films, both of which are original experiments. Furthermore, the GexC1-x material was doped with Al to determine the effect of doping on the film properties. Surprisingly, up to a certain level of Al incorporation in the film, photon absorption increased and this promoted better photoconductivity. For photovoltaic and other electro-optic applications the (Ge, C) system is promising since the addition of C to Ge reduced the lattice dimensions enough to allow a lattice match to silicon, while it increased the bandgap to be close to that of c-Si. The hollow cathode technique allows for the growth of these GeC films with properties which cannot otherwise achieved. The hollow cathode technique has plasmas ignited in both the Ge and the C nozzles and when doped, in the Al nozzle. Samples have been grown with various Ge, C, and Al sputtering rates and different rates of gas flow for both Ar and H2. The substrates in all cases were crystalline Si wafers, either with native oxide remaining (indicated by OX or OXIDE) on the curves or crystalline Si etched with HF just prior to insertion into the vacuum system. Table I shows the experimental parameters for the films referred to in this paper. In this
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