Person:

Recht, Daniel

We investigate the luminescence of Si supersaturated with S (Si:S) using depth-resolved cathodoluminescence spectroscopy and secondary ion mass spectroscopy as the S concentration is varied over 2 orders of magnitude ((10^{18}–10^{20} cm^{−3})). In single-crystalline supersaturated Si:S, we identify strong luminescence from intra-gap states related to Si self-interstitials and a S-related luminescence at 0.85 eV, both of which show a strong dependence on S concentration in the supersaturated regime. Sufficiently high S concentrations in Si ((>10^{20} cm^{−3})) result in complete luminescence quenching, which we propose is a consequence of the overlapping of the defect band and conduction band.

Highly supersaturated solid solutions of selenium or sulfur in silicon were formed by ion implantation followed by nanosecond pulsed laser melting. n+p photodiodesfabricated from these materials exhibit gain (external quantum efficiency >3000%) at 12 V of reverse bias and substantial optoelectronic response to light of wavelengths as long as 1250 nm. The amount of gain and the strength of the extended response both decrease with decreasing magnitude of bias voltage, but >100% external quantum efficiency is observed even at 2 V of reverse bias. The behavior is inconsistent with our expectations for avalanche gain or photoconductive gain.