Shah, M; (2014) Excitation Mechanisms in erbium-doped silicon-rich silicon oxide. Doctoral thesis , UCL (University College London).

Abstract

Since the invention of the first silicon transistor in 1947, the electronics industry has grown at a rapid rate, famously predicted and guided by Moore’s law. However, it has recently become apparent that satisfying Moore’s law is becoming increasingly difficult; we are now approaching the fundamental limits of device miniaturization and device speed, and alternative solutions for this problem are continuously being pursued. Over the past couple of decades, silicon photonics has emerged as a promising alternative solution. By carrying data through photons instead of electrons, many of the problems faced in an electronic device become irrelevant in an equivalent photonic device. The challenge of silicon photonics is to demonstrate lasing in a material that is compatible with existing CMOS processing technology, namely silicon. Light emission from silicon, however, is very inefficient, due to its indirect electronic bandgap. Silicon nanostructures, on the other hand, exhibit far higher light emission efficiencies, which has been attributed to quantum confinement effects. Erbium is one of the most interesting rare earth impurities for optical functionality, as it emits photons at 1.54µm, the wavelength that corresponds to minimum attenuation in silica fibres. However, erbium has a relatively low excitation cross section, and narrow excitation bands, necessitating expensive lasers for amplifier operation. It has been found that, by co-doping erbium with silicon-nanocrystals (Si-ncs), far higher excitation efficiencies of erbium can be attained, along with broadband excitation, through energy transfer from excited Si-ncs. To date, a clear understanding of the physics involved in the excitation mechanism is lacking. In this thesis, I identify erbium excitation processes in the Er doped silicon rich silicon oxide material, through photoluminescence (PL) spectroscopy. In particular, time resolved decay data of erbium emission is analysed through exponential fitting and rate equation modelling. The significance of Purcell enhanced radiative emission, and Er ion-ion interactions are highlighted. Furthermore, a characterisation study of Er doped silicon rich silicon oxide thin films will be carried out, revealing the significance and differences between defect, Si- nanocluster, and Si-nanocrystal sensitisation of Er ions. The prospects of device fabrication will also be discussed.

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