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.
The prospects for a thin film amorphous silicon based integrated photonic technology spanning materials, devices, and physics are described. Impurity implantation is an effective technique for the preparation of permanent refractive index patterning due to the very high solubility limits of the amorphous phase. Methods of preparing films of the requisite thickness and smoothness for photonic application have been identified. Other experiments suggest that there is a light induced refractive index change of sufficient magnitude for patterning light adaptive and/or light defined optical elements. Two light induced refractive index changes, one fast and one slow, were observed in amorphous silicon materials. These changes were observed over temperatures ranging from room temperature to 250 degree(s)C and do not appear to diminish with increasing temperature over this range. Simulations were used to elucidate the physics of light induced change. Several classes of thin film devices were developed which span a wide range of functionality.
The prospect of hydrogenated amorphous silicon based photonic thin film material and devices is introduced. The hydrogen content of hydrogenated amorphous silicon controls its refractive index. Hydrogen content and therefore the refractive index patterning techniques and possibilities are described. For example, regions of a growth surface exposed to a hydrogen radical (and/or ion) flux have increased optical band gap and decreased refractive index. By careful implementation of hydrogen control the preparation of 3-D photonic crystal films on a wide variety of substrates including single crystal silicon and flexible polymer becomes possible. The size scales on which it is possible to pattern the hydrogen content are appropriate for the preparation of photonic crystal films and bulk materials designed to interact with the infrared, visible light, or micro-wave electro- magnetic spectrums. The optical band gap of amorphous silicon depends on specific hydrogenated structures. The relatively independent patterning of the band gap and refractive index makes possible an extensive array of optical devices.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.