Amorphous Silicon in Microphotonics

Abstract

Amorphous silicon (amorphoussilicon (a-Si)siliconamorphous (a-Si)) is an attractive high-refractive-index material for waveguide applications because of its flexible deposition conditions, which do not rely on the existence of crystalline silicon. However, a-Si can exhibit significant propagation losses due to unsaturated bonds in the silicon. Adding hydrogen will reduce those losses, but hydrogen itself can out-diffuse due to elevated processing temperatures. In this chapter, we describe the progress that has been made in the last 20 years with a-Si waveguides and related passive and active photonic devices. We review the basic mechanisms of loss in a-Si and solutions for reducing propagation losses to an acceptable level. We then discuss passive a-Si devices such as ring resonators and multimode interferometer (MMI) power splitters. In the last section, we focus on active devices that use a-Si-based waveguides.