Passivation of p-n junction in crystalline silicon by amorphous silicon

Hydrogenated amorphous silicon, a-Si:H, is shown to be an excellent passivant for crystalline silicon (c-Si) p-n junctions. A two-orders-of-magnitude reduction in reverse leakage current from that of a typical thermal oxide passivated junction is obtained. This is achieved through a lowering of the interface state density by hydrogenation of the c-Si surface. Superior bias-temperature stability of the passivated junctions also is observed. There is evidence that the hydrogen in the bulk of the a-Si:H can act as a hydrogen reservoir for rehydrogenation of the interface between c-Si and a-Si:H. Thermal stability of the a-Si:H is adequate for temperatures up to 500°C for 30 min, which is sufficient for most device-processing requirements. Above 550°C, significant dehydrogenation from both the interface and the bulk a-Si:H regions and an increase in leakage are observed. The passivation properties were assessed through studies of the current-voltage and current-temperature characteristics of the p-n junctions.