Optical transitions coupled with the two-dimensional surface subbands

The optical transitions taking place between two-dimensional surface subbands and bulk bands of semiconductors are investigated. It is shown that such transitions lead to a creation either of free carriers in bulk bands and two-dimensional surface subbands, or of excitonic states coupled with two-dimensional subbands. The theoretical description of these processes is elaborated. The low-temperature photoluminescence spectra of the GaSe crystals are investigated and it is shown that a variation of the surface potential leads to the dissociation of excitons coupled with two-dimensional surface subbands. The probability of such dissociations is evaluated. It is shown that these dissociations can lead, in particular, to an increase in the efficiency of the solar energy conversion in hydrogen energy. (C) 1998 Elsevier Science B.V. All rights reserved.