Report on Army Research Office Grant W911NF-10-1-0442 (Massachusetts Institute of Technology)

Abstract

Abstract : In collaboration with ARDEC Benet Labs, Rensselaer Polytechnic Institute (RPI), and Harvard University, we conducted a systematic investigation of sub-band gap optical response in hyper-doped silicon. Doping silicon with non-equilibrium concentrations of chalcogen atoms (i.e., hyperdoping) yields remarkably strong optical absorptance to wavelengths as long as 5 microns, and measureable photodiode response at wavelengths as long as 1.5 microns. Despite these remarkable properties, photodiode response remains weak at sub-band gap wavelengths shorter than 1.5 microns, and negligible at longer wavelengths. We adopt a systematic approach to understand sub-band gap optical absorption in hyper-doped silicon. We provided a diagnosis of hyper-doped silicon's potential to achieve the Army's goal of 100% situational awareness, especially in the shortwave-infrared portion of the optical spectrum. Specifically, we performed multiple-wavelength spectroscopy to determine the location and bandwidth of states within hyper-doped silicon's band gap; contact-less measurements of carrier concentration to determine whether sub-band gap photon absorption generates mobile carriers; and measurements of the photo-excited carriers transport properties. Using this knowledge, we provide an assessment for hyper-doped silicon as a potential sensor material at wavelengths important to specific Army operational goals, including eye-safe operation (lambda approx. 1550 nm), replacement of InGaAs (lambda less than 1700 nm), and other applications (lambda greater than 2000 nm).