Study of Si-nanocrystals-based light-emitting devices

• Main Author: Chen, Tupei.
• Other Authors: School of Electrical and Electronic Engineering
• Format: Research Report
• Language: English
• Published: 2009
• Subjects: DRNTU::Engineering::Electrical and electronic engineering::Nanoelectronics
• Online Access: http://hdl.handle.net/10356/16923
• Institution: Nanyang Technological University

In this project, Si nanocrystals embedded in dielectric matrix have been synthesized with the technique of Si ion implantation and plasma enhanced vapor deposition (PECVD). The resulting structure of the synthesized films embedded with nc-Si have been characterized by the techniques of transmission electron microscopy (TEM), x-ray diffraction (XRD), secondary ion mass spectroscopy (SIMS), and x-ray photoelectron spectroscopy (XPS), spectroscopic ellipsometry (SE), and photoluminescence (PL) and electroluminescence (EL) measurements. XPS has been employed to study the evolution of chemical structures corresponding to the oxidation states as a function of annealing. Optical properties, including the optical constants and dielectric functions, of Si nanocrystals in the photon energy range of 1-5 eV have been experimentally determined and modeled for the first time from the SE analysis. The bandgap expansion and dielectric suppression of Si nanocrystals have been also investigated. Strong room-temperature PL emission has been observed from SiO2 thin films embedded with nc-Si synthesized with Si ion implantation and subsequent thermal annealing. It has been found that thermal annealing at 1100 degree Celcius exhibits PL related to the formation of nc-Si. In this work, size-dependent PL bands with the peak wavelength ranging from ~720 to ~960 nm have been realized through adjusting the implantation energy and implanted Si ion dose. The PL energy decreases with the increasing nanocrystal size in accordance with the quantum confinement concepts. However, the size-dependent PL could not originate from the direct band to band transition of nc-Si. Based on the knowledge of band structure of nc-Si obtained in this work, the size-dependent PL band could be attributed to the indirect band-to-band transition of the nc-Si assisted by the Si-O vibration at the interface of nc-Si/SiO2. In addition, the evolution of PL mechanisms of Si+-implanted SiO2 thin films under different annealing conditions has been investigated. Visible and near infrared (IR) EL has been observed from a metal–oxide–semiconductor-like (MOS-like) structure with Si nanocrystals embedded in the gate oxide fabricated with low-energy ion implantation. Different nanocrystal distributions are achieved by varying the implanted Si ion dose and implantation energy. The nanocrystal distribution is found to play an important role in the EL. The influence of the applied voltage, the implantation dose, and implantation energy on the luminescence bands has been investigated. The current transport in the material system follows a power law, and it is determined by the concentration and distribution of the nc-Si in the oxide film. A linear relationship between the EL intensity and the current transport is observed. The current transport evolves with both the concentration and distribution of the nc-Si, and so does the EL. With the knowledge of the dependence of the transport on the concentration and distribution of the nc-Si, one can predict the effect of the implantation recipe on the EL intensity.