Investigation of carrier transport and collection characteristics for GaAs-based betavoltaic batteries

This paper presents a simulation model to predict the performance of GaAs-based betavoltaic batteries with a p–n junction structure, in which the carrier transport and collection characteristics were studied. First, the electron–hole pair generation rate in the GaAs material under the irradiation of a 63Ni source was calculated using the Monte Carlo codes. Furthermore, by simulating the energy band structure, electric field distribution, and current density distribution in batteries with the finite element analysis software COMSOL Multiphysics, we analyzed the effects of structure parameters on the output performance. Our simulation results showed that the short-circuit current density (Jsc), open-circuit voltage (Voc), maximum output power density (Pm), and energy conversion efficiency (η) of the batteries are significantly affected by the thicknesses and doping concentrations of the p-region and n-region (Hp-GaAs, Hn-GaAs, Na, and Nd). The optimized GaAs-based battery with an Hp-GaAs value of 0.1 μm, an Hn-GaAs value of 9.9 μm, an Na value of 3.98 × 1016 cm−3, and an Nd value of 1 × 1015 cm−3 can achieve a Pm value of 0.080 μW/cm2. The related Jsc, Voc, and η values are 0.234 μA/cm2, 0.49 V, and 1.55%, respectively. When the top and bottom heavily doped layers are introduced, the Pm value of the battery is enhanced by 7.5% compared to that of the battery without heavily doped layers due to the formed drift fields.