Amorphous-crystalline silicon interface prepared using DC saddle-field pecvd

Abstract

The DC saddle field glow discharge method was used to deposit a-Si:H in order to passivate c-Si surfaces. The process temperature and the thickness of the a-Si:H films were varied. In addition subsequent annealing of the smaples were studied. Passivation quality of the a-Si:H overlayers were studied by measuring the effective minority carrier lifetime in the heterostructures as a function of the minority carrier density in the c-Si wafer. These results are then used to model the surface recombination mechanism in our samples. The defect density and the charge density at the interface are inferred which helps us to distinguish between the effects of electric field and chemical passivation at the interface. It is shown that for our intrinsic a-Si:H samples improvements in surface passivation are directly correlated with the reduction of interface defect density and field effect passivation is minimal. We have achieved surface passivation with effective carrier lifetime > 5 ms for a 40 nm intrinsic a-Si:H sample deposited at a process temperature of 200 o C. It is also demonstrated that subsequent annealing, at 240 o C, of the samples which were prepared at process temperatures < 240 o C drastically increases the effective lifetime.