P-POLARIZED REFLECTANCE SPECTROSCOPY - A HIGHLY SENSITIVE REAL-TIME MONITORING TECHNIQUE TO STUDY SURFACE KINETICS UNDER STEADY-STATE EPITAXIAL DEPOSITION CONDITIONS

This paper describes the results of real-time optical monitoring of ep itaxial growth processes by p-polarized reflectance spectroscopy (PRS) using a single wavelength application under pulsed chemical beam epit axy (PCBE) condition. The high surface sensitivity of PRS allows the m onitoring of submonolayer precursor coverage on the surface as shown f or GaP homoepitaxy and GaP on Si heteroepitaxy as examples. In the cas e of heteroepitaxy, the growth rate and optical properties are reveale d by PRS using interference oscillations as they occur during growth. Superimposed on these interference oscillations, the PRS signal exhibi ts a fine structure caused by the periodic alteration of the surface c hemistry by the pulsed supply of chemical precursors. This fine struct ure is modeled under conditions where the surface chemistry cycles bet ween phosphorus supersaturated and phosphorus depleted surfaces. The m athematical model describes the fine structure using a surface layer t hat increases during the tertiarybutyl phosphine (TBP) supply and decr eases during and after the triethylgallium (TEG) pulse, which increase s the growing GaP film thickness. The imaginary part of the dielectric function of the surface layer is revealed from the turning points in the fine structure, where the optical response to the first precursor pulse in the cycle sequence changes sign. The amplitude of the fine st ructure is determinated by the surface layer thickness and the complex dielectric functions for the surface layer with the underlying bulk f ilm. Surface kinetic data can be obtained by analyzing the rise and de cay transients of the fine structure.