Highly-conductive B-doped nc-Si:H thin films deposited at room temperature by using SLAN ECR-PECVD

Abstract

Highly-conductive B-doped nc-Si:H was deposited at room temperature by using electron cyclotron resonance (ECR) plasma enhanced chemical vapor deposition (PECVD) with a slot antenna (SLAN ECR-PECVD) for low-temperature-process solar-cell and thin-film-transistor (TFT) applications. A novel SLAN ECR plasma source has a higher ionization rate compared to a RF plasma source, with a plasma density of ~1011 cm−3 at 1 mTorr. Spectroscopic ellipsometry, I–V, Raman spectroscopy, and UV-Vis spectroscopy measurements were used for the characterization. B-doped a-Si:H deposited at low H2 flow rates ( 30 sccm), it becomes highly conductive, 0.9–1.7 S/cm. The dopant activation energy is very low at 0.028 eV in spite of the room-temperature deposition. At 40 sccm of H2, the crystalline volume fraction of the film becomes 65%, and the crystal size is around 9.26 nm. Both the crystallinity and the crystal size increase with increasing flow of H2 and enable dopant activation. The optical bandgap varies from 2.07 to 2.35 eV with increasing H2 flow, and the film is useful as a wide-bandgap p-layer for use in p-i-n solar cells or for low-temperature-process TFT applications.