Modelling electronic spectra of crystals in electric fields with various orientations

The present work considers the electronic spectra of a simple two-dimension al (2D) cubic crystal and a three-dimensional (3D) GaAs crystal when a cons tant electric field is applied. The 2D case is treated within the empirical tight-binding (TB) model, taking one s-orbital per atom and accounting for the interactions with neighbours up to fourth order. For the 3D case a sem iempirical sp(3)s* TB model is used, taking into account the spin and first neighbours. The local densities of states (LDOSs) have been calculated for different field intensities, showing that for a sufficiently strong field the 2D LDOS turns into the ID LDOS corresponding to chains perpendicular to the field orientation. This is a novel observation achieved through the us e of neighbours farther than the first. The 3D LDOS of a GaAs crystal proje cted by a strong field on the [001] direction is found to coincide with the 2D LDOS of an isolated atomic layer.