A device for producing electricity. In one embodiment, the device comprises a doped germanium or a doped GaAs substrate and a plurality of stacked material layers (some of which are doped) above the substrate. These stacked material layers, which capture beta particles and generate electrical current, may include, in various embodiments, GaAs, InAlP, InGaP, InAlGaP, AlGaAs, and other semiconductor materials. A radioisotope source generates beta particles that impinge the stack, create electron-hole pairs, and thereby generate electrical current. In another embodiment the device comprises a plurality of epi-liftoff layers and a backing support material. The devices can be connected in series or parallel.