Interfacial Stresses and Strains Effect on Band-Gap Emission from Silicon

Czochralski silicon wafer materials were interfaced with silica films formed by sol-gel deposition and thermal annealing. Under optimal annealing conditions ($\sim$700 $^{\circ}$C), stresses in the silica films induce variations in elastic strains on the order of 1\% in the silicon. Concomitantly, emission of band-gap photons at 1.1 eV observed by photoluminescence is increased by two orders of magnitude relative to unperturbed silicon. The enhancement in photon emission is produced by band-gap modulations estimated as $\sim$0.1 eV. Elastic reversibility of the strains is inferred from recovery of relatively weak photon emission for annealing above the glass reflow temperature of deposited silica films ($\sim$950 $^{\circ}$C). Films with largest stress variations exhibit enhanced absorption signatures in the infrared and broadening of Si-O-Si stretching vibrations. Examples of Si-based photonics based on the observed effect will be presented.