Atomic layer deposition of erbium-doped thin films for silicon integrated waveguide amplifiers

Over the past decade, silicon photonics has emerged as one of the most studied and developed fields in photonics and optoelectronics. One of the major reasons for this is to improve the well-developed microelectronic and telecommunication technologies by integrating optical functionalities on integrated circuit chips, which can enable faster response time, wider transmission bandwidth and lower power consumption in low-cost, highly compact silicon-based optical interconnects. However, some of the essential active on-chip functionalities, such as light emission and amplification, have not yet been realized in silicon photonics with cost-effective methods. Therefore, silicon photonics industry is currently in high demand for cost-effective active materials at telecom wavelengths to continue the rapid development of not only the integrated circuit technology, but also the optical telecommunication networks. This thesis presents a simple yet exceptional configuration that combines novel atomic layer deposition processes for strongly-doped erbium-alumina thin films and state-of-the-art silicon nitride waveguides to form cost-effective integrated waveguide amplifiers operating at telecom wavelengths. The results of this thesis are divided into three main parts. The first part presents a novel plasma-enhanced atomic layer deposition process for strongly-doped erbium-alumina thin films, which enables up to ~3.5 at.% Er-incorporation into alumina before severe concentration quenching occurs. Photoluminescence characterization of the fabricated thin films demonstrates up to 1580 % photoluminescence enhancement at telecom wavelengths with excited state lifetime as long as ~5 ms. The second part combines the optimized plasma-enhanced atomic layer deposition process for strongly-doped erbium-alumina and state-of-the-art silicon nitride slot waveguides to demonstrate ultra-high on-chip optical gain at telecom wavelengths. With both experimental and theoretical analysis, up to ~20 dB/cm net modal gain per unit length is demonstrated in sub-mm to mm-long integrated slot waveguides. The third part demonstrates an improved, faster and more reliable thermal atomic layer deposition process for strongly-doped erbium-alumina thin films, which enables up to ~3.9 at.% Er-ions to be incorporated into alumina with excited state lifetime as long as ~5.8 ms. By combining the improved atomic layer deposition process for erbium-alumina and state-of-the-art silicon nitride strip waveguides, cost-effective integrated waveguide amplifiers are produced with up to ~14 dB/cm net modal gain per unit length over an entire sub-cm waveguide channel. The waveguide amplifiers fabricated and demonstrated in this thesis exhibit the highest net modal gain per unit length ever reported for planar waveguides integrated on silicon, which shows tremendous progress in developing efficient active building blocks on the silicon photonic platform.