RECONSTRUCTION OF THE GAAS(001) SURFACE-INDUCED BY SUBMONOLAYER BE DEPOSITION

As a p-type dopant, Be induces changes in the reconstruction of the Ga As(001) surface. This has been studied as a function of Be coverage up to 0.5 monolayer (ML) by reflection high-energy electron diffraction (RHEED) and scanning tunneling microscopy (STM). Under standard molecu lar beam epitaxy conditions, the RHEED pattern continuously changes wi th increasing Be coverage from the starting (2 x 4) via a (2 x 3) to a (1 x 2) symmetry. This transition is characterized by a gradual decre ase of both, the intensity of the 1/2-order spots (first in the [<(1)o ver bar 10>] then in the [110] azimuth) and the spacing of the 1/4-ord er spots (in the [<(1)over bar 10>] azimuth). STM images reveal that t he surface is composed of both As and Ga/Be terminated domains. The fo rmer reconstruct from (2 x 4) to (2 x 3) units, the latter from (2 x 3 ) to (1 x 2) units. Electron-counting arguments suggest that the domai n type and size are determined by the requirement that the excess elec tron density is balanced by the acceptor density of the incorporated p -type Be doping. (C) 1997 Elsevier Science B.V.