Characterization of a Boron Carbide Heterojunction Neutron Detector
Abstract
New methods for neutron detection have become an important area of research in support of national security objectives. In support of this effort, p-type B(sub 5)C on n-type Si heterojunction diodes have been built and tested. This research sought to optimize the boron carbide (BC) diode by coupling the nuclear physics modeling capability of GEANT4 and TRIM with the semiconductor device simulation tools. Through an iterative modeling process of controllable parameters, optimal device construction was determined such detection efficiency and charge collection were optimized. This allows an estimation of expected charge collection and efficiency given a set of operating parameters that include: silicon resistivity, BC resistivity, BC thickness, silicon thickness, applied bias, and collection contact. Charge collection was maximized with high bias operation of thin BC layers on thin silicon substrates of low resistivity (<10 omega-cm), while the capture efficiency was maximized for thicker BC layers. Additionally, the effects of neutron damage on BC diodes were studied to determine damage thresholds and resulting device performance and lifetime. The major limitation found for device performance was the increase in the leakage current (~340% at a thermal fluence of 9.7x10(exp 13) n cm(exp -2)) in the 8k omega-cm diode. Type inversion was not measured at the total fluence levels achieved, but the 8k omega-cm diode effective carrier concentrations (N(sub eff)) decreased by 30% at a total thermal fluence of 7.5x10(exp 13) n cm(exp-2) (1x10(exp 13) 1 MeV neutron equivalent). For the same irradiation conditions, the 20k omega-cm diode N(sub eff) decreased by 57%. These results indicate that the hardness of the diodes can be improved with low resistivity silicon substrates.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 24, 2011
- Accession Number
- ADA538569
Entities
People
- James E. Bevins
Organizations
- Air Force Institute of Technology