Progress in deposited refractive index engineered materials and devices

The design latitude for photonic engineering in amorphous silicon-based materials is great because of the very high solubility limits for impurities in the amorphous phase and the large change in refractive index that accompanies impurity infusion. Our recent experimental work found both the classical dynamic light induced refractive index changes and a rich set of light induced changes in the optical constants of amorphous silicon materials not found in classical systems. Included in the changes unique to amorphous silicon are slow light induced structure changes triggered by an above gap illumination induced defect's effect on the relaxation of surrounding structure. There are also very fast refractive index changes associated with above gap illumination which our recent work reports are not be associated with heating nor is it directly related to the slow change. Additionally, it has long been known that amorphous silicon has a strong electro-absorption response near the band edge. The fast changes and the electro-absorption are explained in terms of a simple tetrahedral bonded silicon model in which the electron coherence length is limited and the optical transitions are indirect. This model provides a framework for the development of a photo-active integrated photonic technology based on amorphous silicon.