Raman monitoring of ternary compound formation: ZnSxSe1-x on GaAs(100)

Epitaxial layers of ZnSxSe1-x were grown on GaAs(100) at room temperature by molecular beam epitaxy (MBE) using compound sources for the evaporation of both ZnSe and ZnS. The formation of the ternary compound was monitored on-line by taking Raman spectra from the sample surface, i.e. continuously during the growth process. The spectra display ZnSxSe1-x-related scattering processes up to third order under resonant excitation using the 2.808 eV (441.6 nm) emission line of a HeCd laser. From the frequency positions of the ZnSe- and ZnS-like longitudinal optical (LO) phonon modes the sulfur content x was determined. The Raman scattering intensity displays a characteristic modulation upon deposition time due to Fabry-Perot interference of the incident as well as the scattered light. From the period of this modulation, the growth rate was calculated. Furthermore, photoluminescence (PL) spectra were taken in situ using the 3.81 eV (325 nm) emission line of the HeCd laser. They display the near band edge emission of the ZnSxSe1-x layer in the blue spectral region.