TRANSIENT SURFACE-STATES DURING THE CBE GROWTH OF GAAS

We report the occurrence of a transient surface state during the initi al stages of CBE GaAs(001) growth. The stare was detected in real-time reflectance (R) and reflectance anisotropy spectroscopy (RAS) growth monitoring. At low growth rates, less than 1 mu m/h, beam equivalent p ressure (BEP) of triethylgallium (TEG)< 2.5 x 10(-5) mbar there was no change in R and the RAS signal changed from its pre-growth value unde r arsenic stabilisation at the growth temperature to its ''during grow th'' value upon admission of the TEG, with the familiar monolayer osci llations. At higher TEG BEPs there was a rapid increase in R at all mo nitoring wavelengths, followed by a monotonic decay to its pre-growth value. This transient increase in R was accompanied by a change in the RAS signal, the magnitude and sign of which varied with wavelength. T he initial increase in R is shown to be associated with the developmen t of a metallic-like surface whereas the changes in the RAS signal are consistent with the formation of Ga dimers.