Insituspectroscopic ellipsometry of GaAs(001) surface reconstructions

GaAs(001) surface reconstructions prepared by molecular-beam epitaxy were studied in situ by spectroscopic ellipsometry (SE) and reflectance difference spectroscopy (or reflectance anisotropy spectroscopy) as a function of temperature. Simultaneous measurements of the dielectric function by SE and the reflectance difference {Δ}r/r allow us to identify surface and bulk-related contributions to the optical anisotropy {Δ}{ε}=ε_110-ε₁₁₀. For the (2×{}4), the c(4×{}4), and the (4×{}2) reconstructions we find resonances in Im({Δ}{ε}) at 2.9, 2.6, and 2.25 eV at T=80 ^∘{}C. Although the resonance at 2.9 eV coincides with the E₁ bulk transition and also shows the same temperature dependence, they can be distinguished, because the surface contribution changes the sign when switching from the (2×{}4) to the c(4×{}4) reconstruction and the bulk contribution remains the same. {} 1996 The American Physical Society.