Migration-enhanced pulsed chemical beam epitaxy of GaP on Si(001)

Abstract

In this paper, we present results on the heteroepitaxial growth of GaP on Si by migration enhanced pulsed chemical beam epitaxy (PCBE) using additional hydrogen and filament assisted techniques. For the real-time monitoring we applied a new technique, p-polarized reflectance spectroscopy (PRS) which provides information on the bulk, interface and surface properties of the grown GaP/Si heterostructures. The monitoring is initiated close to the Brewster angle for the substrate material, achieving high sensitivity in the initial phase of heteroepitaxial overgrowth. The bulk properties and growth rate are monitored using the quarter wave periodic structure in the reflectance based on interference in the film. The surface vicinity properties are monitored by the periodic fine structures in the intensity of the reflected light, which are correlated with the switching cycles of the metalorganic precursor pulses and are amplitude-modulated in accord with the repeat cycle of the heteroepitaxial growth process. Additional information regarding the surface roughness was revealed by scattered light measurements during the growth of the film. The results of real-time monitoring of nucleation and growth are combined with results of the ex-situ characterization of the GaP/Si heterostructure by cross-sectional transmission electron microscopy (TEM) and atomic force microscopy (AFM) studies to gain an understanding of the critical phase, in which the silicon surface becomes sealed by a contiguous epitaxial film of GaP. The defects formed in the GaP film during this phase determine the quality of the epilayers obtained upon prolonged growth.