Properties of Hydrogenated Amorphous Silicon Prepared by ECR Plasma CVD Method

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Abstract
Hydrogenated amorphous silicon (a-Si:H) films were prepared by the microwave electron-cyclotron-resonance (ECR) plasma CVD method using SiH4 gas without intentional substrate heating. The influence of the deposition conditions in the ECR plasma CVD method on the properties of a-Si:H films was studied and the properties were correlated with plasma optical emission spectra of similar deposition conditions. Photoconductivity of ∼10-6 (Ω cm)-1 under simulated AM1 (100 mW/cm2) illumination was obtained for the as-grown film with an optical gap of ∼2.1 eV at the SiH4 gaspressure of 2×10-4 Torr. The photoconductivities, the optical gaps and the B values estimated from optical absorption measurements were widely changed when SiH4 gas pressure condition was changed. Infrared absorption spectra also showed that the Si-H2 stetching mode at ∼2100 cm-1 and (Si-H2) n wagging mode at ∼845 cm-1 increased as SiH4 gas pressure increased. Measurements of optical emission spectra in the SiH4 ECR plasma showed that the emission intensity ratio of Si (288 nm) to SiH (414 nm) was larger than that in conventional RF plasma CVD, and that the photoconductivities and optical gaps increased as this ratio increased.