Phononic amorphous silicon: Theory, material, and devices

The prospect of using phonons in amorphous silicon to convey information from one location to another is investigated. It is known that the phonon lifetime in amorphous silicon is anomalously long and the phonon diffusivity is relatively large as compared to crystal silicon and other materials. A commercial Raman spectrometer measuring from the film side operating at 785 nm was used in conjuncture with a 470 nm bias light illuminating the glass side of amorphous silicon films deposited onto glass substrates. All measurements were conducted at liquid nitrogen temperature. Analysis indicates a phonon diffusion length of a least 0.5 μm. These results directly lead to tantalizing prospects for phonon engineered amorphous silicon technology.