Electrical properties of amorphous and epitaxial Si-rich silicide films composed of W-atom-encapsulated Si clusters

Abstract

We investigated the electrical properties and derived the energy band structures of amorphous Si-rich W silicide (a-WSin) films and approximately 1-nm-thick crystalline WSin epitaxial films (e-WSin) on Si (100) substrates with composition n = 8–10, both composed of Sin clusters each of which encapsulates a W atom (WSin clusters). The effect of annealing in the temperature range of 300–500 °C was also investigated. The Hall measurements at room temperature revealed that a-WSin is a nearly intrinsic semiconductor, whereas e-WSin is an n-type semiconductor with electron mobility of ∼8 cm2/V s and high sheet electron density of ∼7 × 1012 cm−2. According to the temperature dependence of the electrical properties, a-WSin has a mobility gap of ∼0.1 eV and mid gap states in the region of 1019 cm−3 eV−1 in an optical gap of ∼0.6 eV with considerable band tail states; e-WSin has a donor level of ∼0.1 eV with sheet density in the region of 1012 cm−2 in a band gap of ∼0.3 eV. These semiconducting band structures are primarily attributed to the open band-gap properties of the constituting WSin cluster. In a-WSin, the random network of the clusters generates the band tail states, and the formation of Si dangling bonds results in the generation of mid gap states; in e-WSin, the original cluster structure is highly distorted to accommodate the Si lattice, resulting in the formation of intrinsic defects responsible for the donor level.