Thorium-228 as emitting source for InGaP/GaAs-based heterojunction alphavoltaic cells

Alphavoltaic nuclear batteries are promising long-life power sources. Their effective performance is strongly dependent on the design of the device structure and the used semiconductors as well as on the appropriate radiation source involved in the power conversion process. Currently, semiconductor heterojunction structures are promising in improving the efficiency of nuclear micro-batteries. In this study, we designed and evaluated a micro-power alphavoltaic nuclear battery consisting of an In0.49Ga0.51P/GaAs alphavoltaic heterostructure using a lab-made software. The device active area is 1 cm(2) and the assumed energy source is Thorium-228 (Th-228) which emits alpha particles with an average kinetic energy of 5.423 MeV. We used a comprehensive analytical model to extract the energy conversion efficiency of the cell by simulating its current density-voltage J(V) and output electric power P(V) curves. Our analysis took into account the reflection of the incident alpha particles from the front surface, the ohmic losses, the limits of the space charge region, and the metallurgical border effects. To optimize the device performance, we investigated a wide range of doping concentrations and surface recombination velocities in both the back and front regions while also assuming different values of the radioisotope apparent activity density. Under irradiation by a 3.2 mCi/cm(2)Th(228) source, the energy conversion efficiency of the cell is 8.83%, while the maximum output power density is 18.15 & mu;W/cm(2). The obtained results are very encouraging showing that the use of Th-228 coupled with an appropriate In0.49Ga0.51P/GaAs heterojunction could be a suitable solution for designing alphavoltaic batteries with a useful output power.