Material and growth mechanism studies of microcrystalline silicon deposited from SiF₄/H₂/Ar gas mixtures¹

Hydrogenated microcrystalline silicon is of great interest as the intrinsic layer in thin film solar cells. It is generally accepted that optimized cells use an I-layer with a crystalline fraction ranging from 50% to 70%. We report here on the use of fully crystallized layers deposited from SiF ₄/H₂/Ar gas mixtures. A V_OC of 536 mV and a J_SC of 25.4 mA/cm² have been obtained in PIN solar cells using a fully crystallized intrinsic material. Fourier transform photocurrent spectroscopy measurements show that the films have a very low defect density down to 5.1 × 10¹⁴ cm^-3. The role of H₂ during deposition has been investigated: it is demonstrated that H₂ is needed to remove F by forming HF molecules. When all atomic F has been removed from the plasma, the remaining atomic H can then contribute to μc-Si:H growth.