Vacancies in amorphous silicon: A tight-binding molecular-dynamics simulation

Vacancies formed in amorphous silicon are studied through the tight-binding molecular-dynamics method. Physical properties, such as the electronic density of states and volume change of a single vacancy at various sites, are obtained. The bond-angle deviation and the average valence charge of the atoms next to a vacancy are analyzed and found to be closely related. Even though vacancies at high density can be annihilated at room temperature, no migration of vacancies is observed in the simulations up to 450 K. Divacancy in amorphous silicon is found to behave similarly to a single vacancy of other types. Whereas there are many similarities between the vacancies in amorphous silicon and those formed in crystalline silicon, significant differences are found in some of their properties.