Disorder on GaAs(001) surfaces prepared by molecular beam epitaxy

Measurable disorder exists on GaAs(001) surfaces during MBE even though these surfaces subsequently incorporate into exceedingly well-ordered bulk GaAs lattices. We have used reflection high energy electron diffraction (RHEED) to characterize this disorder. On the As stabilized surface obtained at 850 K, some of the fractional order beams are broadened indicating that there is antiphase disorder present on the surface. Models of this disorder are presented. In addition, if the growth is stopped by shuttering the Ga flux both integral and quarter order beams sharpen, indicating that a second type of disorder exists. From the lengths of the RHEED streaks we determine that during growth the long range order in the twofold direction is about 500 Å. About 10 min after growth is stopped, the extent of order in this direction increases to 3000 Å. At a given As flux the ordering process is slightly temperature dependent over the narrow range that this disordered 2 × 4 exists. At lower temperatures, the disordered structure switches to a C (4 × 4), at higher temperatures to a 1 × 4.