Reconstruction of the GaAs(001) surface induced by submonolayer Be deposition

As a p-type dopant, Be induces changes in the reconstruction of the GaAs(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 molecular beam epitaxy conditions, the RHEED pattern continuously changes with increasing Be coverage from the starting (2 × 4) via a (2 × 3) to a (1 × 2) symmetry. This transition is characterized by a gradual decrease of both, the intensity of the 1/2-order spots (first in the [110] then in the [110] azimuth) and the spacing of the 1/4-order spots (in the [1¯10] azimuth). STM images reveal that the surface is composed of both As and Ga/Be terminated domains. The former reconstruct from (2 × 4) to (2 × 3) units, the latter from (2 × 3) to (1 × 2) units. Electron-counting arguments suggest that the domain type and size are determined by the requirement that the excess electron density is balanced by the acceptor density of the incorporated p-type Be doping.