A stacked betavoltaic battery using a lateral-growth-smoothed BGaN intrinsic region
Munson, Charles E.
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An investigation into possible ways to increase the efficiency of betavoltaic battery technology by using a novel material, BGaN, by utilizing the stacking of PIN devices, and to research designs to increase the radioactive source efficiency by reducing self-absorption. One major issue in the development of nitride-based PIN devices is maximizing efficiency with a strong electric field across the intrinsic region. The high carrier concentration of intrinsic GaN due to unintentional doping reduces the possible PIN electrical field strength and results in high recombination of electron-hole pairs generated. By using BGaN, we expect to reduce this carrier concentration and increase overall device efficiency. Additionally, most betavoltaic battery designs only consider beta particle collection on one side of the radioactive source. This gives a maximum overall efficiency of only 50%, since energy that emits away from the device cannot be collected. By creating a stacked package design, we expect to efficiently collect beta particles emitted in all directions by the radioactive source, thereby potentially doubling the overall battery efficiency. Since Ni-63 in particular is highly susceptible to self-absorption, steps to reduce these effects should be taken to help increase the efficiency of the radioactive source itself. Although this does not affect the overall device efficiency, it does have an impact on the maximum potential power output of the device given a fixed amount of Ni-63 material. Various designs have been proposed by us that aim to reduce the effects of self-absorption in the radioactive source, and we expect to achieve up to 95% source efficiency from our designs. Finally, a study demonstrating the durability of our materials and devices will be discussed, which show that exposure to radioactive Ni-63 over 100 years will not appreciably degrade the performance of our betavoltaic battery. This ensures our battery could maintain a high level of power and efficiency for at least 100 years. We will discuss the simulations and designs that we created, which are necessary to achieve these results, as well as discuss the fabrication and packaging of a Ni-63 betavoltaic battery that is used to realize the designs. A comparison of the modeling predictions with experimental data will be explored, demonstrating the accuracy of our models and the quality of our materials and designs.