Two-dimensional and quasi-two-dimensional surface excitons

Full text: Reflectance, electroreflectance, photoluminescence and electroluminescence spectra are well known physical methods in investigation of bulk and surface excitons of materials. ZnO and CdTe in A2B6 compound semiconductor are representatives of the biggest and the smallest ion connections, which have direct electronic junctions corresponding to wave vector K=0. The experimental investigations are done in various temperatures either in non-contacts or on ZnO- and CdTe-electrolyte interface. The results of investigations allow to explain a number of specialties of surface excitons' behaviour, incomprehensible till nowadays. Determined the changes of surface excitons behaviour connected with ZnO and CdTe surface electronic states, chemical adsorption specialties and surface potential value. Evaluated the band energy values of surface excitons either in two-dimensional and quasi two-dimensional excitons depended on surface electronic states of local radius, effective mass values and screening degree. This approach allows to explain band energy values of experimentally founded surface excitons, which have less than theoretical evaluations. Surface and bulk excitons lines have different temperature dependence. For example, on the reflectance spectra CdTe the intensivities of bulk excitons lines surpass the investigations of surface excitons lines in the 4-30K temperature sphere. The corresponding lines of surface excitons are obvious only in the 30-300K temperature sphere, when the intensivities of bulk excitons lines are considerably decreasing