Structures and photoluminescence properties of silicon thin films prepared by pulsed ion-beam evaporation

Synthesis of photoluminescent (PL) Si thin films is explored using an intense pulsed ion-beam evaporation (IBE) technique. The deposition of Si was performed at a vacuum condition of ∼10−2 Pa in a simple scheme. Well-crystallized Si thin films have been obtained as revealed by high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD). Visible light emission in blue–green range was observed from the samples under excitation of a 325 nm He–Cd laser (3.8 eV) at room temperature. The thin films were composed of relatively large crystals with an average size around 20 nm, above the range predicted using a quantum confinement model proposed for Si nanocrystals. The PL was subsequently studied with a hydrofluoric acid (HF) erosion test, intended to diminish the effect of Si oxides on the samples, where no PL shift was found except for deterioration in PL intensity after the post-treatment of samples. Furthermore, the experimental PL spectra can be consistently deconvolved into four subbands with centers at 2.88, 2.75, 2.55, and 2.36 eV. All the PL subbands are ascribed to Si oxide-defect bands irrelevant to the quantum confinement model.