OPTICAL INVESTIGATIONS OF SURFACE PROCESSES IN GAP HETEROEPITAXY ON SILICON UNDER PULSED CHEMICAL BEAM EPITAXY CONDITIONS

Surface processes during the heteroepitaxy of GaP on Si under pulsed c hemical beam epitaxy conditions were investigated simultaneously by th e optical methods reflectance difference/anisotropy spectroscopy, p-po larized reflectance spectroscopy (PRS), and laser light scattering. Ou r studies were performed during both cyclic and interrupted growth, wh ere the surface was exposed to individual pulses of the precursors tri ethylgallium (TEG) and tertiarybutylphosphine (TBP). The data show tha t the three optical probes provide different perspectives of growth. S everal surface processes exhibit time constants of the order of 1 s. O ne such process is the clustering of Ga atoms, or less likely, of TEG fragments, that occurs with TEG exposure. The optical data also show t hat TBP dealkylation occurs essentially instantaneously upon arrival a t the surface, and that TEG dealkylation is the rate-limiting step. Th e PRS data exhibit fine structure that shows that heteroepitaxial grow th can be described by a four-phase model consisting of the substrate, a GaP layer, a surface reaction layer containing all adsorbed species not yet incorporated in the growing layer, and the ambient. By assumi ng that this surface layer is very thin we derive approximate equation s that allow us to treat the PRS response quantitatively. (C) 1996 Ame rican Vacuum Society.