Angle-resolved photoemission from As-stable GaAs (001) surfaces prepared by MBE

Angle-resolved photoemission measurements, combined with RHEED, have been made on As-stable, reconstructed (001) 2*4 and C(4*4) GaAs surfaces prepared in situ by molecular beam epitaxy. A dangling-bond surface state having predominantly sp z character has been identified on the 2*4 surface, and a model for this structure based on dimerisation of adjacent surface As atoms proposed. The bridge bond between As atoms is tilted, and although largely of p x character, has a p z component. The phasing of the dimer sequences is responsible for the orthogonal reconstruction. These conclusions have been based on an atomic orbital approach, since band-structure calculations have not been performed for the reconstructed surface. Some similarity has been observed, however, between the observed dispersion of a deeper lying back-bond state and that predicted from a calculation of the ideal 1*1 band structure by considering back-folding effects arising from reconstruction.