Nanoelectronic properties of Si and Ge: A semi-empirical approximation

A semi-empirical nearest-neighbor tight-binding approach, that reproduces the indirect band gaps of Si and Ge crystalline, has been applied to study the electronic band dispersion relation of Si and Ge nanowires (NWs). The NWs are modeling by free standing, infinitely long and homogeneous NWs cross sections with the wire axis along the zaxis. The calculations show that Si NWs keeps the indirect bandgap while Ge NWs changes into the direct bandgap when the wire cross-section becomes smaller. Also, the band gap enhancement of Si NWs showing to quantum confinement effects is generally larger than that of similar-sized Ge NWs, confirming the larger quantum confinement effects in Si than in Ge when they are confined in two dimensions.