Visible photoluminescence at room temperature from a-Si:H films grown by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition

Hydrogenated amorphous Si (a-Si:H) films were grown without external heating by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition (UHV-ECRCVD) and structural/optical properties were characterized. Visible red photoluminescence (PL), centered around the wavelengths of ∼700 nm, is obtained from the as-grown samples at room temperature. Strong oscillation of PL spectra is observed in the films grown on oxidized Si substrates, which is believed to originate from Fabry-Perot interference effect. As-grown a-Si:H films do not contain Si nanocrystals, and a large amount of (SiH ₂) _n(polysilane) bonding is found. PL intensity depends on deposition conditions, but it usually becomes stronger as the polysilane-content in the as-grown film increases. When the samples are annealed at 350 °C, integrated PL intensity is quenched almost completely as the polysilane content falls off abruptly. Based on these results, possible luminescence mechanisms are discussed.