Design and performance considerations for dual-sided microstructured semiconductor neutron detectors

Abstract

Thin-film-coated solid-state thermal neutron detectors were replaced in recent decades with the Microstructured Semiconductor Neutron Detector (MSND) technology. The basic device structure of the MSND involves micro-sized trenches that are etched into a vertically-oriented pvn-junction diode that are backfilled with a neutron converting material. Neutrons absorbed within the converting material induce fission of the parent nucleus, producing a pair of energetic charged-particle reaction products that can be counted by the diode. The deep-etched microstructures of the MSND yield good neutron-absorption efficiency and reaction-product counting efficiency, resulting in a 6-10x improvement in intrinsic thermal-neutron detection efficiency over thin-film-coated devices. Performance of present-day MSNDs are reaching an efficiency plateau; streaming paths between the conversion-material backfilled trenches, allow a considerable fraction of neutrons to pass through the device undetected. Dual-Sided Microstructured Semiconductor Neutron Detectors (DS-MSNDs) have been developed that utilize a complementary second set of trenches on the back-side of the device to capture streaming neutrons. This work investigates several of the fundamental design structures that can be etched into the semiconductor material, including repeated front-side and back-side patterns and inverse microfeature patterns. Results from MCNP6 simulations of DS-MSNDs show that intrinsic thermal-neutron detection efficiencies are often double that of their MSND counterparts and greater than 80% intrinsic thermal-neutron detection efficiency is theoretically possible with a 1.5-mm thick device.