Abstract
Synthesis and characterization of nanocrystalline silicon (nc-Si) deposited by plasma enhanced chemical vapor deposition method are reported. Optical and microstructural studies are carried out by UV-vis absorption spectroscopy, photoluminescence (PL), X-ray diffraction, high resolution transmission electron microscopy, selected area electron diffraction and Raman spectroscopy measurements. Two PL bands observed at peak energies of 1.86 eV and 2.23 eV. An intense debate as to whether the visible PL at room temperature originated from nc-Si as quantum confinement (QC) or defect state. We have used electron spin resonance and hydrogen (H-2) passivation processes to distinguish between defect state and excitons confined to the nc-Si as the source of the PL. We find that the origin of the PL in the sample can be controlled with the aid of ultra-violet (UV) irradiation to introduce defects, making them as the origin of the PL and then hydrogen passivation remove the defects, resulting in PL from QC states. i.e., Switching it from defect-related in the as-crystallized state to QC after passivation, and back to defect related after subsequent irradiation. The observations of the light emissions from nc-Si at energy of 1.8-2.5 eV should be very important for novel optoelectronic device applications of Si-based materials. In addition, this work opens up the possibility of growing nc-Si thin films at low deposition temperature with well-controlled PL origin. (C) 2014 Elsevier B.V. All rights reserved.