Electronic properties and impurity levels in filtered cathodic vacuum arc (FCVA) amorphous silicon M.M.M. Bilek*, W.I. Milne Department of Engineering, University of Cambridge, Trumpington Street, Cambridge CB2 1PZ, UK Abstract The electronic properties of silicon films deposited by filtered cathodic vacuum arc (FCVA) from silicon cathodes have been studied and correlated with growth conditions. Films with the best electrical properties were deposited at elevated temperature and low background pressure of hydrogen. Room temperature photo-conductivities of around 10 -6 (Qcm) -1 were measured at AM1 illumination. Unstable arc operation and re-triggering of the arc during deposition resulted in films with the highest defect densities, indicating that the defects are due, at least in part, to sputtered impurity atoms. Calculations supporting this suggestion are presented and measures to reduce the levels impurities are discussed.  1997 Elsevier Science S.A. Keywords: Amorphous; Silicon; Vacuum arc; Impurities 1. Introduction Amorphous silicon has attracted much research interest since the early 1970s when the first good quality, dopable thin films were produced using the now commercially estab- lished glow discharge technique [1,2]. The relatively inex- pensive manufacturing process and reasonably good semiconducting properties have made a-Si:H the material of choice for a variety of commercial devices such as thin film transistors and solar cells. Despite its success glow discharge a-Si:H has one major disadvantage which com- promises the performance of the devices in which it is used. Its semiconducting properties are unstable and tend to degrade over time especially under the influence of bias stress or exposure to light. These instabilities are attributed to the presence of excess hydrogen. As little as 1 atomic % of hydrogen is sufficient to remove the localised mid-gap states created by dangling bonds in a-Si, the remaining ~5– 10% contained in device quality glow discharge a-Si:H serves only to reduce lattice strain by reducing the average coordination number [3]. The motivation for examining novel high impact energy methods of production for amorphous silicon, such as the vacuum arc, is the possibility of producing device quality material with low levels of hydrogen and hence improved stability. Recently De et al. [4] showed that films deposited from energetic (1–6 keV) ionised silicon clusters and hydrogen ions had a hydrogen content of ≤10% and improved stability. The particular attraction of the vacuum arc technique stems from its high deposition rates, relatively low cost and nearly 100% ionisation rate, as well as its ability to produce energetic ions. It has been demonstrated in a previous work that amor- phous silicon thin films with a variety of micro-structures can be produced using a filtered cathodic vacuum arc (FCVA) [5,6]. In all cases the reported electronic properties have not been good enough for the material to be considered for use in electronic devices. In this paper we examine the electronic properties and attempt to identify the causes of the poor semiconducting behaviour. Calculations of sputter- ing in FCVA systems and the high levels of metallic impu- rities in the films suggest that a high level of plasma impurities is an inherent problem with the vacuum arc tech- nique which makes it unsuitable for fabrication of quality semiconductors. Ways in which this problem might be over- come are discussed in detail. 2. Experimental details The FCVA system used to deposit the silicon thin films Thin Solid Films 308–309 (1997) 79–84 0040-6090/97/$17.00  1997 Elsevier Science S.A. All rights reserved PII S0040-6090(97)00551-8 * Corresponding author. Tel.: +1 223 330192; fax: +1 223 332662; e-mail: mmmb@eng.cam.ac.uk