In situ Raman studies during the epitaxial growth of ZnSe layers on GaAs(110)

Abstract
ZnSe was deposited onto ultrahigh vacuum cleaved GaAs(110) using a single molecular beam source. The substrate temperature during growth was varied between room temperature (RT=300 K) and 820 K. In addition, some samples were annealed at various temperatures up to 870 K after the ZnSe deposition. Raman spectra were taken in situ after each deposition and after the annealing steps. Under resonant excitation strong scattering signals of the deposited ZnSe are observable for coverages as low as approximately 20 Å. Fröhlich induced scattering of the ZnSe longitudinal optical phonon dominates the spectra, while the deformation potential scattering of the ZnSe transverse optical phonon is very weak. For nominal equal exposure of approximately 1600 Å ZnSe, the layer thickness decreases dramatically with increasing substrate temperature Ts. For Ts ≳ 670 K no ZnSe is detectable, instead Raman features occur which are most probably due to the formation of Ga2Se3. Annealing of a deposited ZnSe layer leads to changes explainable by the presence of Ga2Se3 at the interface. From complementary ex situ spectroscopic ellipsometry measurements a dielectric function and thicknesses of the ZnSe films are derived.

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