LASER-SURFACE DIAGNOSTICS OF GAAS GROWTH-PROCESSES .2. REFLECTANCE ANISOTROPY STUDIES OF GAAS GROWTH BY MBE

The relationship between reflectance anisotropy (RA) signals and As or Ga coverage on GaAs (100) has been investigated by monitoring the RA response through a series of surface reconstructions generated under MBE growth conditions. Under As-rich conditions for which RHEED indicated c(4 x 4) reconstruction the substrate was heated to promote As2 desorption and distinct desorption transients were observed superimposed upon an approximately monotonic variation in the RA signal which correlate with the observation of the c(4 x 4)As to (2 x 4), (2 x 4) to (3 x 1) and (3 x 1) to (4 x 2)Ga RHEED transitions. These phase transitions were observed to be reversible. It is suggested that these phase transitions involve three distinct types of As species each resulting from the unique nature of each reconstruction, and that the experiment performed here may be thought of as an "optical" thermal desorption experiment.