A novel solid state self-powered neutron detector

Abstract

Detection of nuclear materials is critical in preventing traffic of illicit nuclear materials. Several methods that are based on detection of spontaneous or induced emission of fission neutron are considered. Efficient fast and thermal neutron detectors are generally required. For some applications these detectors must have fast response and should be deployed with large or small detection area. This work expands upon the basic concept of coating a p-n junction solar cell with a neutron detection layer that typically employs either 6 Li or 10 B. 10 B has a larger absorption cross section and results in higher detection efficiency. When an incident neutron interacts with 10 B, it releases an α-particle and a 7 Li ion; this α-particle excites electron-holepairs in the silicon p-n junction. This work investigated a variety of different silicon trench/pillar/hole geometries in combination with the 10 B filling or coating; thermal neutron detection efficiencies as high as 30% are projected. It utilizes trenches spaced as closely as 2 µm and 50 µm deep. Simulations predict that when these single layer detectors are bonded in a multiple layer configuration, efficiencies in the range of 90% could be achieved. Along with nuclear and electrical simulations, a highly controllable deep-reactive-ion-etching (DRIE) recipe is developed for trench/pillar/hole etching. The ability to create p-n junctions along those trenches is presented. Trenches and pillars as small as 2 µm by 2 µm are fabricated and p-n junctions are created along their surface. Smooth, uniform trenches are ready for trench refilling procedures.