Identification and control of crystalline nuclei facets imparting to the breaking of symmetry selection rules of optical phonon modes in GaP/Si (001)

Abstract

The complex interfacial structural issues associated with hetero-polar epitaxial integration of GaP on Si(001) are resolved by improving the kinetics of gallium and phosphorous adatoms during the initial nucleation process. This is achieved through the use of Raman spectroscopy as a feedback mechanism. The peak intensity ratio of forbidden (transverse optical)-to-allowed (longitudinal optical) phonons of GaP under unpolarized Raman scattering is contemplated as an initial guide to ascertain the relative density of defect-mediated non-(001) GaP facets. The azimuthal-angle dependent polarized Raman spectroscopy is then applied to identify and quantify the nucleation of higher-index non-(001) ({111} and {112}) faceted islands in the nucleation layer and their propagation in the overgrown structures. The nucleation of GaP adatoms on the Silicon surface at ∼525 °C leads to a smooth surface and substantially suppresses the defect-mediated facets. The optimal mobility and controlled adsorption of adatoms of Ga and P on the substrate surface under intermediate nucleation kinetics foster the charge-neutral interface, and hence the defect-suppressed two-dimensional layer growth of GaP. The proposed Raman spectroscopy methodology emerges as a rapid and economical alternative to existing in situ reflection anisotropy spectroscopy and high-resolution transmission electron microscopy techniques for structural identification. This method of growth optimization can also be applied to other III-V polar semiconductors to achieve high-quality and efficient monolithic integration of devices on existing Si technology.