Molecular-Dynamics Study of Dimer Formation on a GaAs (001) Surface at Low Temperatures

The molecular-dynamics simulation of the formation of dimers for the case of the low-temperature (001) reconstruction of a GaAs surface terminated in Ga or As atoms is employed using the analytical potential, which takes into account σ- and π-bonds between atoms. The values of the decrease in the potential energy of atoms during the formation of the surface of an isolated dimer are found, and it is discovered that the potential energy of an atom in the As dimer is lower by several tenths of eV than that in the Ga dimer. In the temperature range of 25–40 K, the kinetics of the initial stages of the formation of Ga dimers is studied, and it is obtained that the characteristic energy of thermal activation of the formation of single isolated Ga dimers is ~29 meV and lower than the same value for As dimers (~38 meV). In the temperature range of 28–37 K, the time constants characterizing the average rate of the conversion of a single dimer into a chain of two dimers are estimated. For double Ga and As dimers, the reciprocal values of these times turn out to be in the ranges of 1011–1012 and 109–1010 s–1, while similar parameters for the formation of single dimers lie in the range of 4 × 106–108 and 1.4 × 106–7.4 × 107 s–1.