MODELING STEP BUNCHING FORMED ON VICINAL GAAS(001) ANNEALED IN ASH3 AND HYDROGEN AMBIENT

A detailed analysis of the surface morphology of step bunching formed by annealing in AsH3 and hydrogen has been carried out on substrates w ith various miscut directions. The results show that branches, by whic h we refer to step bunchings that do not run in the substrate miscut d irection, form on most of the substrates and for most of the annealing conditions, suggesting that they have a relatively low free energy an d compose an intrinsic component of this step bunching. Also these bra nches are not randomly located on the surface but have a strong tenden cy to align side by side. In order to understand these experimental re sults, we propose a qualitative model designated as the ''chain reacti on model.'' This model is founded on the fact that during annealing st eps can only move by exchanging step-edge atoms with other steps. By t his model we can explain the main characteristics of this step bunchin g: why the step bunching does not grow infinitely in size and why bran ches have a strong tendency to align side by side.