Small electric power cells based on the direct conversion of kinetic energy of alpha particles into electricity have been proposed. These cells are expected to function continuously over long times and at temperatures from -250 to 600 °C. They would be made from semiconductors that are stable at high temperatures (most likely GaAs or SiC). The a-particle sources in these cells will likely be made from curium-244, the radioactivity of which is characterized by a half-life of about 18 years and consists nearly entirely of a particles. The proposed cells could be useful as power sources for low-power electronic circuits that are required to operate for long times without recharging or external wire power connections, and without relying on sunlight. Potential outer-space and terrestrial applications could include electronic circuits for spacecraft on long interplanetary or deep-space missions, hearing aids, and surgically implanted medical electronic devices.
Earlier attempts at utilizing a particles to generate electricity have resulted in limited success because of poor planning and lack of proper device designs. Therefore, the planned development of the proposed cells will include studies of factors that affect power-generation efficiency and of the ability of the cells to survive lattice damage induced by impinging a particles. Computer simulations of the effects of different levels of doping of the semiconductors will be performed in an effort to find optimum device designs, and innovative and device engineering is planned to minimize lattice damage from a particles to maximize device lifetimes and reliabilities.
A basic power cell according to the proposal would include a thin-film a-particle source sandwiched between two p/n diodes (see figure). One key aspect of design that would clearly distinguish a cell of this type from, say, a photovoltaic cell would be the choice of diode dimensions so that a particles of the given initial kinetic energy ( ≈ 5.9 MeV for a 244Cm source) do not stop in the active device volume. The reason for this choice is that a particles cause severe lattice damage in the vicinities of their stopping locations because they lose large fractions of their kinetic energy just before stopping.
Therefore, in the proposed design, outer regions of "dead" semiconductor material would be provided and the dimensions of the p, n, and outer regions would be chosen so that the a particles would come to rest in the outer regions. Although some lattice damage is still expected to occur in the active regions, it has been observed in recent experiments that such damage is continuously annealed during ionization processes in semiconductors.
This work was done by Jagdishbhai Patel of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com under the Electronic Components and Systems category.
NPO-20654
