EFFECTIVE-MASS SUPERLATTICE - SURFACE-STATES AND ZERO-ENERGY GAPS

The electronic structure of a terminated effective-mass superlattice ( EMSL) is investigated taking into account the effect of the EMSL surfa ce (i.e. the EMSL/substrate interface). Special attention is paid to t he conditions under which two neighbouring miniband edges cross each o ther, which results in the vanishing of a corresponding mini-gap for c ertain EMSL bulk parameters (the so-called zero energy gap conditions) . This is shown to influence considerably the surface electronic struc ture of EMSL and, in particular, to affect the existence of surface st ates. It is found that usually a surface state appears within one of t he mini-gaps opening at the bulk band crossing point, so this mini-gap does not effectively exist, while the other mini-gap exhibits no surf ace-related features and, therefore, is well defined. The importance o f the obtained results for the device applications of EMSL is pointed out. (C) 1997 Elsevier Science Ltd.