On the surface passivation of c-silicon by RF sputtered Al2O3 for solar cell application

Abstract

In this contribution we investigated the surface passivation properties of Al2O3 deposited by RF sputtering on c-silicon substrate. MIS capacitors with Al2O3 as dielectric were fabricated and characterized. Post deposition anneal in N2 ambient for 20 min was carried out to activate the passivation. Fixed charge, interface defect density and minority carrier lifetimes were evaluated from the C-V, G-V and C-t characteristics of the MIS capacitor respectively to study the level of surface passivation. It has been demonstrated that by optimizing various sputtering process parameters such as power and base pressure etc. high level of passivation can be achieved for RF sputtered alumina. High level passivation of Al2O3 is attributed to high minority carrier lifetimes. Negative fixed charge density (Qf) as high as 5 × 1012 cm−2 and interface defect density (Dit) as low as 1.85 × 1011 eV−1 cm−2 have been achieved. Minority carrier lifetime was observed to vary from 70 to 290 μs for various sputter deposition and annealing processing condition. The obtained carrier lifetimes are comparable to the value achieved for atomic layer deposited Al2O3 which is generally considered to be favorable process for passivation of solar cells.