Deposited Silicon Photonics: Optical Interconnect Devices In Polycrystalline Silicon

Abstract

Silicon photonics has tremendous potential to provide high-bandwidth and low-power data communication for applications such as computing and telecommunication, over length scales ranging from 100 kilometers over fiber to centimeter-length on-chip waveguides. Many silicon photonic building blocks have been demonstrated to date, but critical work remains to determine the best approaches for integrating together silicon photonics with microelectronics. In this thesis, I explore a novel method for integration of silicon photonics on the CMOS platform by using a deposited material: polycrystalline silicon. I will show the first demonstrations of electrically-active optical filters, modulators, and photodetectors in this material. In principle, this material platform would allow for the integration of silicon photonic devices and systems on top of any substrate, including complex CMOS and memory chips or even glass and plastic substrates. In Chapter 1, I introduce the state-of-the-art in silicon photonics, describe several integration schemes under development, and introduce the idea of using deposited materials. In Chapter 2, I demonstrate the use of polysilicon to make integrated microring resonators, and show the integration of different silicon materials together. Chapter 3 discusses the use of polysilicon as both an optical waveguiding layer and an electrode material in slot waveguides for the application of light emitters. Chapter 4 demonstrates the use of a pump-probe experiment to measure the free carrier lifetime in the material and demonstrate all-optical modulation. In Chapter 5, I demonstrate the first high-speed integrated electro-optic modulator in polysilicon, a necessary device for optical transmitters. In Chapter 6, I show how defects inside the same material enable integrated photodetectors at near-infrared telecommunication wavelengths. Chapter 7 shows initial results in adapting the material processing for lower temperatures, necessary for integration on top of CMOS. Finally Chapter 8 concludes with an outlook for the field.