Gallium Phosphide - Silicon Interface: Structure and Anisotropy Investigations

Gallium phosphide thin films on cheap silicon substrates are a promising III-V/IV heterostructure to be used in optoelectronic devices. As an almost lattice matched system with a band gap difference of 1.14 eV it includes applicability for multi-junction solar cells. The present study concerns discontinuities emerging at the boundaries of a GaP thin layer on a silicon substrate. The optical anisotropy of the (001) interface has been determined by an optical model applied to reflectance anisotropy spectroscopy measurements of the GaP/Si heterostructure. Density-functional calculations of the interface have been performed with both, the pseudopotential plane wave code ABINIT [1] and the all-electron augmented plane wave code Wien2K [2]. The study distinguishes between the Ga-rich and the P-rich interface termination. At the perfectly flat interface, the latter exhibits higher stability as indicated by the work of separation. More complex interface models also consider defects. The calculated density of states projected onto in-plane directions gives an indication for anisotropy. It aims at distinguishing interface termination and defects as origin of the experimentally observed reflectance anisotropy. [1] www.abinit.org [2] www.wien2k.at