Electronic states and optical transitions in small Si quantum boxes

Electronic and optical properties of small Si quantum boxes (QBs) with hydrogen saturators (referred to as a N-x X N-y X N-z structure, where N-x N-y and N-z, are the number of Si monolayers along the [100], [010] and [001] directions, respectively) are studied using the extended Huckel-type nonorthogonal fight-binding method. It is found that a clear transition between the bulk-like and surface-like conduction band (CB) edge states takes place alternately by changing N-z, among others, in the 5 X 5 X N-z (N-z = 5,7,9,...) QBs, resulting in an oscillation behavior in band gap and oscillator strength. The occurrence of the surface-like CB edge state, which is responsible for the enhanced oscillator strength, is found to be ascribed to an inter-hydride interaction between the trihydride units at the side of the (00 (1) over bar) surface. (C) 2002 Elsevier Science Ltd. All rights reserved.