INSITU MONITORING OF HETEROSTRUCTURE GROWTH BY OPTICAL SPECTROSCOPIES - CDS ON INP(110)

Raman and photoluminescence spectroscopies were applied in situ during the molecular beam epitaxial (MBE) growth of CdS layers on ultra-high-vacuum cleaved InP(110) surfaces. The experiments were performed using the emission lines of an Ar+ ion laser which are close in energy to the band gap of CdS. Due to this resonance condition it was possible to detect Raman as well as luminescence signals originating from the CdS overlayer at coverages as low as 2 monolayers (ML). The Raman spectra exhibit features due to scattering by the vibrational modes of CdS. Their number and selection rules confirm the presence of the cubic CdS modification. The Raman spectra are dominated at all coverages by the longitudinal optical (LO) and 2LO phonon scattering intensites. The variation of the 2LO/LO intensity ratio together with shifts in the photoluminescence spectra occurring upon CdS deposition monitors the evolution of the CdS electronic structure. Evidence for the presence of a chemically reacted layer at the interface most likely consisting of In2S3 is also found in both Raman and photoluminescence spectra. Further results obtained from post-growth analysis using ellipsometry, X-ray diffraction, and Rutherford backscattering experiments complement the characterisation of the CdS/InP(110) heterostructure.