Electronic and Optical Properties of Rare-earth Chalcogenides and Pnictides

The dielectric description of crystal ionicity developed by Phillips and Van Vechten has been successfully employed in a wide range of semi-conductors and insulators. However, the applicability of this Phillips and Van Vechten (P. V. V) dielectric analysis has been limited to only simple A(N)B(8-N) compounds. An empirical relationship previously introduced by the authors, relating the electronic properties of zinc blende and complex structured solids to their product of ionic charges, is shown to be applicable with minor modifications to the rock salt structured solids. An alternative approach to the well-known P. V. V. theory has been evolved in order to understand the electronic and optical properties such as heteropolar gap (E-c), average energy gap (E-g), crystal ionicity (f(i)) and optical dielectric constants (epsilon(infinity)) of REX (RE = rare earth metals, X = S, Se, Te, P, As and Sb). The estimation is based on the approximate inverse relationship between the electronic properties and the product of ionic charges of these compounds. The evaluated values are in better agreement with the modified P. V. V. theory.