Making silicon devices responsive to infrared light

January 6, 2014

A laser beam is used in the lab to test the gold-hyperdoped sample of silicon to confirm its infrared-sensitive properties (credit: Jonathan P. Mailoa et al.)

A new system developed by researchers at five institutions, including MIT, could eliminate many limitations in methods to develop detectors that are responsive to a broad range of infrared light. Such detectors could form sensitive imaging arrays for security systems, for example.

The new system works at room temperature and provides a broad infrared response, says associate professor of mechanical engineering Tonio Buonassisi.

It incorporates atoms of gold into the surface of silicon’s crystal structure in a way that maintains the material’s original structure. Additionally, it has the advantage of using silicon, a common semiconductor that is relatively low-cost, easy to process, and abundant.

The approach works by implanting gold into the top hundred nanometers of silicon and then using a laser to melt the surface for a few nanoseconds. The silicon atoms recrystallize into a near-perfect lattice, and the gold atoms don’t have time to escape before getting trapped in the lattice.

Its efficiency is probably too low for use in silicon solar cells, Buonassisi says. However, this laser processing method might be applicable to different materials that would be useful for making solar cells, he says.

The research was funded by the U.S. Army Research Office, the National Science Foundation, the U.S. Department of Energy, and the MIT-KFUPM Center for Clean Water and Energy, a joint project of MIT and the King Fahd University of Petroleum and Mining.

Abstract of Nature Communications paper

Room-temperature infrared sub-band gap photoresponse in silicon is of interest for telecommunications, imaging and solid-state energy conversion. Attempts to induce infrared response in silicon largely centred on combining the modification of its electronic structure via controlled defect formation (for example, vacancies and dislocations) with waveguide coupling, or integration with foreign materials. Impurity-mediated sub-band gap photoresponse in silicon is an alternative to these methods but it has only been studied at low temperature. Here we demonstrate impurity-mediated room-temperature sub-band gap photoresponse in single-crystal silicon-based planar photodiodes. A rapid and repeatable laser-based hyperdoping method incorporates supersaturated gold dopant concentrations on the order of 1020 cm−3 into a single-crystal surface layer ~150 nm thin. We demonstrate room-temperature silicon spectral response extending to wavelengths as long as 2,200 nm, with response increasing monotonically with supersaturated gold dopant concentration. This hyperdoping approach offers a possible path to tunable, broadband infrared imaging using silicon at room temperature.