Effect of Pressure on Bonding Environment and Carrier Transport of a-Si:H Thin Films Deposited Using 27.12 MHz Assisted PECVD Process

Investigation of carrier transport in hydrogenated amorphous silicon (a-Si:H) thin films deposited at various pressures (0.03 - 0.53 Torr) using 27.12 MHz assisted high frequency Plasma Enhanced Chemical vapor Deposition (PECVD) process is presented. From results of Steady State Photocarrier Grating (SSPG) the carrier diffusion length was found to vary from 0.098 - 0.189 μm. Moreover a direct influence of ambipolar diffusion length was observed with the transport mechanism for deposition pressure in the range (0.13 - 0.53 Torr). There was a correlation observed for photosensitivity and microstructure parameter with mobility lifetime (μτ) product and diffusion length of carriers. Diffusion length and μτ product were observed to be maximum (0.189 μm and 0.471 x 10 −8 cm 2V−1) for the film having high photosensitivity (7.2x10 3) deposited at a rate ∼1.39 A/s at 0.53 Torr deposition pressure. In addition to electrical transport properties, the effect of deposition pressure on structural and optical properties was also studied using various characterization tools such as Raman, UV-Vis and infrared spectroscopy.