Real-time optical characterization and control of heteroepitaxial Ga_xIn_(1-x)P growth by P-polarized reflectance

摘要

The characterization and control of thin film growth processes requires improved methods of characterization and understanding of decomposition pathways and surface reaction kinetics under steady-state epitaxial growth involving organometallic precursors. In this contribution we present the application of p-polarized reflectance spectroscopy (PRS) for real-time monitoring and control of pulsed chemical beam epitaxy (PCBE) during low temperature growth of epitaxial Ga_(1-x)InP heterostructures on Si(001) substrates by PCBE, where the growth surface is sequentially exposed to organometallic precursors. During the pulsed precursor supply the surface reaction kinetics can be followed by analyzing a periodically in composition and thickness modulated surface reaction layer (SRL), which is captured in the PR-signals as a fine structure that is superimposed to the interference fringes caused due to the underlying growing film. The optical response is linked to the growth process via a reduced order surface kinetics (ROSK) model and integrated as a control signal in the implementation of filter and control algorithms for closed-loop controlled growth of epitaxial Ga_(1-x)In_xP heterostructures on Si(001) substrates. The control concept has been applied for thickness and compositional graded multi-heterostructure Ga_xIn_(1-x)P epilayers and validated by ex-situ post-growth analysis, showing superior tracking of composition and thickness targest under closed loop controlled conditions compared to films grown using pre-designed source injection profiles (open-loop conditions).