Radiation dosimeter Utilizing an Ultrathin Amorphous-Silicon Layer

This SBIR project will develop a low-cost, temperature-insensitive dosimeter that is both nuclear survivable and compatible with semiconductor-fabrication batch processing. Existing dosimeters based on Geiger counters are relatively low-cost instruments that are inherently radiation-hard because of their insensitivity to gamma-rays and neutrons. They are nevertheless being replaced by dosimeters based on silicon diodes because of ease with which the latter is inexpensively coupled to low-voltage, low-power electronics. Although silicon diodes are highly robust to temperature variations, mechanical shock, and moderate radiation doses, they cannot withstand the extreme conditions experienced during nuclear events because of the sensitivity of the charge transport to defect and trap formation within the sensing structure. One can reduce that sensitivity via the use of an ultrathin (~10 nm) amorphous silicon cavity sensor that: 1) efficiently extracts the radiation-induced carriers from the active region resulting in internal quantum efficiencies greater than 95 %, 2) can operate at low or zero volts, extracting the carriers via thermal diffusion, rather than electric-field drift, 3) has very low dark current because of the relatively high band-gap of amorphous silicon (1.7 eV) and the thin active region, and 4) can be made with low-cost fabrication in conformal sensors via plasma-enhanced chemical vapor deposition (PECVD). The Phase I research is designed to prove the feasibility of using this novel structure as a low-cost, wide-dynamic range dosimeter.