The Relationship Between Reflectance Anisotropy And Electron Diffraction In The Detection Of Reconstruction Changes Occurring At Iii-V Semiconductor Surfaces

We have utilised the technique of reflectance anisotropy (RA) to study the growth of GaAs, AlAs, and InAs on (001) GaAs substrates by molecular beam epitaxy and simultaneously recorded both the RA response and the surface electron diffraction pattern obtained using (RHEED). For macroscopic coverage variations the change in the RA response in all cases appears to correlate exactly with the appearance of a new RHEED pattern. In this respect RA growth "oscillations" are observed which correlate exactly in period with the usual RHEED oscillations observed during growth and can be made to be in-phase with the RHEED oscillations by varying the RHEED collection system. In the case of InAs growth, much more subtle (ca. 0.1 monolayers) coverage variations are easily detectable by RA while the macroscopic(2×4)to(4×2)phase transition which occurs for this system at InAs coverages of ca. one monolayer produces a marked change in both the RA and RHEED response. Since all three systems were studied using the same optical excitation energy (ca. 1.92 eV) and since in all cases the change in the RA response occurred concurrently with the change in the RHEED pattern we question the currently popular theory regarding the nature of the RA response in relation to a supposed local surface dimer state resonant absorption and suggest that geometric factors or longer range surface state resonances may be of equal if not more importance.