A RHEED study of the dynamics of GaAs and AlGaAs growth on a (001) surface by MBE

In this paper we report on RHEED investigations of the damping and recovery of the specular-beam intensity during MBE growth. Our results on the damping behaviour during growth of GaAs and Al0.33Ga0.67As indicate that at a temperature of approximately 610°C the average step density on the surface is at a minimum. At this temperature the change from a (2 × 4) As-stabilized surface to the (1 × 1)(3 × 1) metal-rich surface takes place. We attribute the larger degree of damping at lower temperatures to insufficient ad-atom mobility and thus a high step density on the surface. At temperatures above 610°C we attribute the larger degree of damping to adsorption of gallium atoms on arsenic sites. A purely analytical procedure is used to calculate the recovery rate of the specular-beam intensity. Results are presented for growth termination at various temperatures and at various fractions of monolayer coverage, θGa. It can be concluded that the initial, fast recovery process on the arsenic-stabilized surface is due to Group III kinetics with activation energies generally greater than 1.5 eV. However, a lower activation energy is observed on termination of growth at 12 of a complete monolayer (θGa = 0.5), indicating the recovery process to be then limited by As4 physisorption. The second, slow step in the recovery has activation energies of the order of 5 eV. The initial recovery process on the gallium-rich surface is characterized by lower activation energies, of the order of 0.5 eV. The mathematical analysis presented here allows one to calculate the minimum growth interruption times to obtain smooth surfaces in a straightforward manner.