| AVS 56th International Symposium & Exhibition | |
| Thin Film | Thursday Sessions |
| Session TF-ThA |
| Session: | Next Generation Processing |
| Presenter: | A. Illiberi, Eindhoven University of Technology, The Netherlands |
| Authors: | A. Illiberi, Eindhoven University of Technology, The Netherlands V. Verlaan, Eindhoven University of Technology, The Netherlands M. Creatore, Eindhoven University of Technology, The Netherlands W.M.M. Kessels, Eindhoven University of Technology, The Netherlands M.C.M. van de Sanden, Eindhoven University of Technology, The Netherlands |
| Correspondent: | Click to Email |
We investigated the material properties of expanding thermal plasma deposited a-Si:H thin films, providing a record-low surface recombination velocity of 1.6 cm/s (at injection level of 1 1015 cm-3). a-Si:H thin films with different thicknesses have been deposited at a high deposition rate (1.2 nm/s) on both sides of low resistivity (1-5 Ohm cm), 260µm thick, n- and p-type c-Si FZ wafers. The material properties of a -Si:H films have been characterized by Fourier Transform Infrared diagnostic and Spectroscopic Ellipsometry. The surface passivation of the wafers has been determined by photoconductivity decay measurements of the effective carrier lifetime. The investigation points out that the growth of ETP a-Si:H films begins with the formation of a thin porous layer (< 10 nm) with a refractive index of 3.9 (at 2 eV) and a microstructure parameter (R*) of 0.50. Despite the open network formation at the a-Si/c-Si interface, a 7 nm a-Si:H film achieves a recombination velocity as low as 12 cm/s (at 1·1015 cm-3 injection level on n-type wafers). The good passivation is probably due to the large hydrogen content of the a-Si:H film, which terminates dangling bonds present on the c-Si surface. After this initial growth, a dense a-Si:H network develops with a refractive index of 4.3 (at 2 eV) and R* = 0.03. The surface recombination velocity decreases linearly with the a-Si:H thickness, achieving a record value of 1.6 cm/s (at 1·1015 cm-3 injection level) for 90 nm thick a-Si film on n-type wafers. As compared to hot wire CVD and radiofrequency PECVD techniques, ETP is capable to deposit thin a-Si:H films with outstanding surface passivation at higher temperature (250° C) and higher deposition rate (1.2 nm/s). The stability in time of surface passivation has been investigated. Effective carrier lifetime is found to decrease following a stretched exponential. Photo-electronic properties of a-Si:H are know to relax in time in a similar fashion. These results therefore suggest a correlation between the photo-electronic properties of the a-Si:H/c-Si interface and a-Si:H bulk material.