Study On Variable Temperature Elliptical Polarization Spectra Of Dimensional Thyristor Nanocrystals

Over the past two decades, the field of Si photonics has attracted many attentions. Since bulk crystalline silicon can’t be applied to light emitter, low-dimensional silicon materials have gained more and more research interest because of their light-emitting abilities. Silicon nanocrystals (nc-Si) embedded in SiO2matrix provides probable applications in Si-based optoelectronic devices, memory devices, and single electron devices. It is also promising for achieving optical gain and waveguiding with the advantage of full compatibility with the matured Si technology. In order to know nc-Si better, this work provide a reliable approach to measure the optical properties of nc-Si under different temperature. The main work is shown as follows:1. Spectroscopic ellipsometry (SE) measurement combined with a data processing method was performed, to accurately get the dielectric function spectra (ε=ε1+iε2) of materials at different temperatures. The theory of SE measurement is introduced in this work. A temperature variable sample holder was fixed on the sample stage of the SE equipment for temperature dependent measurement from room temperature to600K with an accuracy of±0.1K. As a result, the optical properties of different sized nc-Si are obtained.2. Four-oscillators-based Lorentz oscillator model and the Maxwell-Garnett effective medium approximation were employed to extract dielectric function of nc-Si and nc-Si:SiO2composite thin film. The variation of the dielectric function with temperature is based on the thermo-optic effect in which the interaction between the phonons and electrons affect the optical properties of the material at different temperature. Electron-phonon interaction is the dominant factor for the band gap reduction with temperature increasing. In addition, the information about temperature properties of nc-Si is useful for the design and fabrication of silicon based devices.3. From ε2spectra, the critical point (CP) E1of2nn,3nm,5nm sized nc-Si samples were determined at different temperature. By plotting the energy of critical points, the E1band-gaps were gained and the parameters of Varshni approximation were fitted too. The result shows that larger sized nc-Si is more sensitive to temperature.