Potential efficiency improvements in fast-neutron semiconductor sensors from finely detailed structuring: A study by simulation including dead layers

The neutron sensor in an active neutron-sensitive personal dosemeter typically comprises a planar silicon diode topped with a converter layer. Neutrons interact in the converter to produce charged particles that are then detected in the diode. However, in the dosimetrically important energy region of a few keV to a few MeV, the efficiency of such devices is small because of the small cross section for producing the charged particles and their very limited range within the converter. The efficiency can in principle be improved by etching fine structures such as trenches or wells in the silicon, and filling these with the converter, so that a considerably larger amount of converter is within one particle range of the silicon. This study quantifies the potential improvements in efficiency for a selection of structure sizes and fast monoenergetic neutron energies. It also investigates how seriously these improvements are degraded if there is a dead layer at the surface of the silicon.