Contents I. Introduction
Alloys of Si, Ge, and C have been attracting the interest of researchers for more than two decades [1]. These materials have found a large variety of applications ranging from optical devices such as detectors and waveguides to state-of-the-art field-effect transistors [2]. This letter focuses on erbium silicide contacts formed on epitaxial layers pseudomorphically grown on Si substrates. The alloys are presently attracting the interest of various research groups for several reasons. First, the semiconductor bandgap can be tuned by varying the C concentration. It has been shown that, when layers are pseudomorphically grown on Si, the resulting in-plane biaxial strain leads to splitting of the electron valleys and down shifting of the twofold degenerate conduction band [3]–[5]. While there is a similar movement occurring in the valence band, it is relatively small with respect to the changes in the conduction band. Both experimental [3], [4] and theoretical [5] studies showed that the bandgap of pseudomorphic on Si is reduced by 65 meV for every 1% of C. Second, the bandgap reduction provides a conduction-band offset, which provides new opportunities in engineering new device structures. Third, provides a new path in strain engineering, since it has a smaller lattice constant than Si. For instance, alloys are currently considered in source/drain regions of n-channel metal–oxide–semiconductor field-effect transistors (MOSFETs) to establish uniaxial tensile strain in the transistor channel for electron-mobility enhancement [6]. The alloys are also of interest as the channel material in future MOSFETs [7], the base region in advanced bipolar junction transistors [8], and the Schottky contact layer in photodetectors [9].
