Modeling the Photovoltage of Doped Si Surfaces

Abstract

Doped Si(111) surfaces have been modeled with a Si slab, and their photovoltage has been calculated with a combination of ab initio electronic structure and density matrix treatments from the steady state solution of the electronic density matrix (DM) for electrons interacting with thermalized lattice vibrations. Densities of electronic states and photovoltage spectra of the silicon surfaces are drastically affected by the presence of p or n doping. We report results on the effect of surface doping by group III (B, Al, and Ga) and group V (N, P, and As) elements, of interest in the study of surface optical properties, for concentrations of doping atoms in the host lattice in the range of 0.5−1.5%, obtained from slab atomic models with several hundred atoms. Analysis of the results provides insight on trends relevant to the absorption of near IR, visible, and near UV light and to measurements of photovoltages and shows some of the trends found for doped bulk Si in experiments at lower dopant densities.