Surface passivation of crystalline silicon by sputter deposited hydrogenated amorphous silicon

This letter shows that intrinsic hydrogenated amorphous silicon (a-Si:H) films deposited by RF magnetron sputtering can provide outstanding passivation of crystalline silicon surfaces, similar to that achieved by plasma enhanced chemical vapour deposition (PECVD). By using a 2% hydrogen and 98% argon gas mixture as the plasma source, 1.5 Ω cm n-type FZ silicon wafers coated with sputtered a-Si:H films achieved an effective lifetime of 3.5 ms, comparable to the 3 ms achieved by PECVD (RF and microwave dual-mode). This is despite the fact that Fourier transform infrared spectroscopy measurements show that sputtering and PECVD deposited films have very different chemical bonding configurations. We have found that film thickness and deposition temperature have a significant impact on the passivation results. Self-annealing and hydrogen plasma treatment during deposition are likely driving forces for the observed changes in surface passivation. These experimental results open the way for the application of sputtered a-Si:H to silicon heterojunction solar cells.