REAL-TIME OPTICAL CHARACTERIZATION OF GAP HETEROSTRUCTURES BY P-POLARIZED REFLECTANCE

The stringent tolerances in the engineering of advanced optoelectronic integrated circuits with respect to control thickness and composition of ultra-thin layers require the development of monitoring and contro l techniques that follow the deposition process with sub-monolayer res olution. These demands led to the development of surface-sensitive rea l-time optical sensors that are able to move the control point close t o the paint where the growth occurs, which in a chemical beam epitaxy process is the surface reaction layer, built up of physisorbed and che misorbed precursor fragments between the ambient and film interface. I n this contribution, we explore the application of p-polarized reflect ance spectroscopy (PRS) in the context of real-time monitoring and con trol of pulsed chemical beam epitaxy (PCBE) Juring low temperature gro wth of epitaxial GaP heterostructures on Si(001) substrates by PCBE. T he effect of periodic alterations in composition and thickness of a su rface reaction lever (SRL) is monitored by PRS as a periodic modulated reflectance amplitude, denoted as fine structure. Using a reduced ord er kinetic model' we demonstrate the linkage of the PRS response towar ds surface reaction chemistry, film growth rate, and film properties. Mathematical control algorithms are introduced that link the PR signal s to the growth process control parameters. (C) 1998 Elsevier Science S.A.