Title: Defect Mediated Sub-Bandgap Optical Absorption in Ion-Implanted Silicon Nano-Wire Waveguide Photodetectors
Description: Silicon has numerous benefits as a photonic integrated circuit platform, including optical transparency from 1.1 Âµm to greater than 5 Âµm, tight optical confinement due to its high index of refraction, high third order non-linearity, and lack of two photon absorption at wavelengths above 2.2 Âµm. Additionally, silicon photonics has the added benefit of decades of fabrication knowledge from the CMOS industry. Despite these advantages, an enormous challenge exists in two areas, optical sources for silicon photonic integrated circuits, and on the other end, optical detectors for silicon photonic integrated circuits. The same bandgap energy that leads to the optical transparency at telecom and mid-infrared wavelengths, limits both generation and detection in this same regime. This dissertation focuses on the detection problem, exploring the use of defect-mediated sub-bandgap optical absorption in ion-implanted silicon nano-wire waveguides. Section I of this dissertation focuses on fabrication and the ion-implantation process, including a primer on Shockley-Read-Hall theory and its application to defect-mediated sub-bandgap optical absorption.

Section II examines the devices for use at telecom wavelengths. In Chapter 4, the fabrication and characterization of metal-semiconductor-metal ion-implanted silicon nano-wire waveguide photodiodes is examined. These devices require minimal fabrication, are compatible with standard CMOS fabrication processes, and exhibited responsivities as high as 0.51 A/W and frequency responses greater than 2.6 GHz. With improved fabrication tolerances, frequency responses of greater than 10 GHz are expected. Chapter 5 examined these ion-implanted photodiodes in a p-i-n configuration as a high speed data interconnect, demonstrating error free operation at 10 Gbs with expected sensitivities approaching that of Ge detectors. Section III extends the above research to longer wavelengths, starting with data reception at 1.9 Âµm in Chapter 6, exhibiting an approximate 5 dB penalty in sensitivity compared to the same diodes at 1.55 Âµm, at a data rate of 1 Gbs, limited by RC due to the 2 mm length of the device.

Chapter 7 goes even further, characterizing Si+ implanted silicon nano-wire waveguides for operation between 2.2 Âµm and 2.35 Âµm. These devices showed responsivities as high as 9.9 mA/W, with internal quantum efficiencies approaching 5%. Chapter 8 concludes with the characterization of Zn+ implanted silicon nano-wire waveguides operating in the same wavelength regime, exhibiting higher overall responsivity, albeit at a much higher reverse bias. These long wavelength devices open up new areas of research for silicon photonics, allowing for CMOS compatible detectors operating into the mid-infrared region, useful for chemical sensing, free-space communications, and medical imaging.