ROLE OF STRUCTURAL AND CHEMICAL CONTRIBUTIONS TO VALENCE-BAND OFFSETSAT STRAINED-LAYER HETEROJUNCTIONS - THE GAAS GAP (001) CASE/

We calculate with the nb initio pseudopotential method the valence-ban d offset (VBO) of GaAs/GaP lattice-mismatched heterojunctions pseudomo rphically grown on GaAsxP1-x(001) substrates (0 less than or equal to x less than or equal to 1). The resulting value of 0.76 eV for the GaP substrate supports the highest among the experimental data available. We show that the VBO for any substrate can be easily obtained from th at calculated for one substrate following standard band-structure theo ry since the interface-dependent contribution to the VBO, which is the electrostatic potential lineup, has no significant variation with the substrate. Such variation, however, can be taken into account accurat ely by a simple analytic scaling law, which is demonstrated here. Fina lly, we show that the VBO of GaAs/GaP (001) is due to structural and c hemical effects, and we propose an operative method for identifying an d separating the two contributions, whose dependence on strain is also discussed. (C) 1996 American Vaccum Society.