Polycrystalline GeC Thin Films Deposited Using a Unique Hollow Cathode Sputtering Technique
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Polycrystalline GeC Thin Films Deposited Using a Unique Hollow Cathode Sputtering Technique R. J. Soukup1, N. J. Ianno1, J. S. Schrader1 and V. L. Dalal2 1
Department of Electrical Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588-0511, USA 2 Department of Electrical and Computer Engineering, Iowa State University, Ames, IA 50011, USA Abstract Experimental results on thin films of the new material GexC1-x, deposited by a unique dual plasma hollow cathode sputtering technique are presented. The most important contribution of this work is that it shows that by using non-equilibrium growth conditions resulting from the hollow cathode technique, one can grow Group IV materials which cannot otherwise be grown using normal CVD or MBE processes. The sputtering is accomplished by igniting a dc plasma in the Ar and H2 gases which are fed through Ge and C nozzles. The GeC films are grown on etched Si (100), on Si with the native oxide and on glass. The films grown on glass were quite disordered, but the films grown on both types of Si substrates were very ordered in nature. This order has been characterized using Xray diffraction (XRD) and Raman spectroscopy. Films with as much as 8% C have been deposited. In order to produce useful GexC1-x films, the C must bond to the Ge at lattice sites. Evidence of this desired GeC bond has been seen using Fourier Transform Infrared Spectroscopy (FTIR), Raman Spectroscopy, and XRD. 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. For photovoltaic and other electro-optic applications the (Ge, C) system is extremely promising since the addition of C to Ge may reduce the lattice dimensions enough to allow a lattice match to silicon, while increasing the band gap close to that of c-Si. Using the hollow cathode technique, one can grow Group IV materials which cannot otherwise be grown using normal CVD or MBE processes. Recently, a significant advancement in the deposition of this material has been achieved by electron cyclotron resonance (ECR) plasma deposition.1,2 Unfortunately, only about 3% C can be incorporated into these films. The use of the hollow cathode plasma jet in the successful growth of semiconductors has been well documented for amorphous hydrogenated silicon, a-Si:H3 germanium, a-Ge:H4 and silicon/germanium, a-SiGe:H.5,6 In this study, the process is slightly different in that the incorporation of hydrogen into the film is not necessarily an objective, though hydrogen is used to assist in the crystalline growth of the GeC films. A
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photo of the system with germanium and carbon nozzles being sputtered is shown in Fig. 1. Samples have been grown with varying Ge and C sputtering rates, different substrate temperatures, different rates of gas flow for both Ar and H2, varying nozzle to substrate distance, and different substrate biases. Films have been grown with the Ge to C power ratio ranging from .75 to 8.25. The most
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