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GaAs (001) surfaces in both metalorganic vapour phase epitaxy (MOVPE) and molecular beam epitaxy (MBE) are studied under As stabilisation as well as during growth by reflectance anisotropy spectroscopy (RAS). During MBE growth reflection high energy electron diffraction (RHEED) measurements are performed simultaneously. As a consequence of the oscillating density of steps during island growth, time resolved RAS measurements show oscillations with monolayer periodicity in both epitaxial systems. In order to separate morphology related and surface reconstruction domain related contributions to RAS oscillations an anisotropic effective medium model is applied. In both MBE and MOVPE domains of reduced As coverage close to the island boundaries are found to be responsible for RAS oscillations. In MBE this typically results in oscillations between spectra belonging to (2 x 4) reconstructions of different mean As dimer density. In MOVPE the surface oscillates between states with an increased and a decreased concentration of G a dimers while c(4 x 4)-like As dimers are still present.') Hardenbergstr.

Exposure of GaAs and InGaAs to PH3 is a standard step in gas switching sequences for metalorganic vapor phase epitaxy (MOVPE) growth of heterostructures in the technologically important GaAsP, InGaP, and InGaAsP material systems. The exchange of group-V atoms was monitored in situ by reflectance anisotropy spectroscopy when GaAs is exposed to PH3. The c(4×4) reconstructed, As-terminated GaAs surface is then replaced by a P-terminated structure. At standard MOVPE growth temperatures and pressures the time constant for this reaction is of the order of 100 ms. The temperature and pressure dependence of the As by P exchange is reported, and the activation energy was determined to be 1.64 eV. It is concluded that PH3 enhances the desorption of As.

In this letter we report on the observation of growth oscillations with monolayer periodicity by ellipsometry. An oscillation amplitude of δ〈ε1〉=0.05 was measured using an optimized spectroscopic in situ ellipsometer whose wavelength was tuned to the 2.65 eV resonance energy of the arsenic dimers covering the GaAs (001) growth surface. The monolayer periodicity was verified by parallel monitoring of the growth with reflectance anisotropy spectroscopy (RAS).

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