Monte Carlo Evaluation of Tritium Beta Spectrum Energy Deposition in Gallium Nitride (GaN) Direct Energy Conversion Devices

Report No. ARL-TR-7082
Authors: Marc Litz
Date/Pages: September 2014; 22 pages
Abstract: In this report, a Monte Carlo nuclear scattering codeMonte Carlo n-particle extended (MCNPX)was used to investigate the possibility of using gallium nitride (GaN) semiconductors for the purpose of converting the low energy β emitted during natural decay of tritium (3H) into electrical current for use in a power source. The shape of the beta decay spectrum differs in isotopes because of screening potentials and forbidden transitions. Therefore the use of average energy or endpoint energy is not sufficient for a detailed understanding of energy deposition in a material. The technique of direct energy conversion (DEC) is considered advantageous with GaN compared to that of silicon carbide (SiC). GaN has a direct band gap material of 3.4 eV compared to the more commonly used SiC with a 3.2-eV indirect band gap. The beta emission spectrum from 3H, directed toward a GaN converter is modeled. A GaN device optimized to stop all β in 3H would be less than 1.5 µ thick. The depletion region in a GaN DEC that would enclose 99% of the charge generated by separated electron hole pairs is calculated to be 700 nm thick for 3H.
Distribution: Approved for public release
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Last Update / Reviewed: September 1, 2014