A density functional theory study on the passivation mechanisms of hydrogenated Si/Al2O3 interfaces

Abstract

Amorphous aluminum oxide (A l 2 O 3) films are known to provide a high-quality passivation on silicon (Si) surfaces which can result in an enhanced efficiency of Si-based solar cells. After deposition of A l 2 O 3 on Si, a certain temperature treatment is needed to activate the highest surface passivation quality. When the applied temperature is exceeded by a certain level, the passivation quality degrades. This behavior is well known in the production of Si-based solar cells. In order to further elucidate the microscopic origin of passivation mechanisms and its interplay with thermal treatments, we investigate four different atomistic Si / A l 2 O 3 interface models by means of density functional theory simulations. As interfacial hydrogen (H) is deemed to play a key role in Si / A l 2 O 3 surface passivation mechanisms and its amount changes during thermal treatments, two of these models contain hydrogen in different amounts; the other two do not contain any hydrogen. The simulations show that both chemical passivation and field-effect passivation depend on the relative amount of hydrogen via partially competing mechanisms. The obtained results provide novel insights into the passivation mechanisms of Si / A l 2 O 3 interfaces. The results are qualitatively compared to the thermally induced activation and degradation of the Si (100) / A l 2 O 3 surface passivation known from experiments.