Influence of SiH4 and pressure on PECVD preparation of silicon films with subwavelength structures

Abstract

Silicon films with subwavelength structures were prepared on flexible polyimide by plasma deposition. Resulting films exhibited high photosensitivity and high stability. The varied parameters were pressure and silane (SiH4) flow, while power, frequency, temperature, and hydrogen (H2) flow were fixed. Pressure was set at 0.7 or 1.3 Torr, while the SiH4 flow rate was set at 10, 50, or 100 sccm. Similar characteristics were observed for the films when the same SiH4 flow rate was used, despite pressure variations. Deposition rate from 0.94 to 5.86 Å/s, optical gap from 1.6 to 2 eV, and embedded nanocrystals in the range of 2–6 nm were the main characteristics of our films. Subwavelength structures from 102 to 287 nm in diameter were observed. These structures scatter the photons and thus improve absorptance, photosensitivity, and mobility-lifetime product. The structural and optoelectronic properties of these films showed a high correlation with the silane concentration obtained from the partial pressure of SiH4 and H2.