Growth monitoring by reflectance anisotropy spectroscopy in MOVPE reactors for device fabrication

Reflectance anisotropy spectroscopy (RAS) has proved its capability to study surface processes during metalorganic vapour phase epitaxy (MOVPE) growth of a variety of III–V compounds. However, these investigations up to now have been mostly restricted to specialized research reactors. Therefore, we studied the feasibility of in-situ monitoring by RAS during growth on two production-type MOVPE reactors: horizontal 2 inch single wafer reactor AIX 200 and Planetary Reactor™ AIX 2000 for 5 × 3 inch. The slight modifications of the reactors necessary to gain normal incidence optical access to the sample do not alter the properties of the grown materials. While in the horizontal reactor the strain-free optical window allows one to obtain well-resolved RAS spectra the signals in the multiwafer reactor are affected by the anisotropy of the ceiling plate. Even in this case RAS spectra can be extracted. First measurements on rotating samples in the horizontal reactor demonstrate the possibility to obtain RAS spectra by multitransient spectroscopy. As an application monitoring of the growth of p-type layers for the base of GaInP/GaAs hetero-bipolar-transistors (HBTs) is discussed. The linear electro-optic effect (LEO) gives information on doping type and doping level. Time-resolved transients at specific energies are used to study the impact of different switching schemes on the properties of the base-emitter interface.