Patent Number: 
Section: claims

1. A device for producing electricity, comprising:a substrate;a plurality of stacked material layers above the substrate, the plurality of stacked material layers comprising,a base layer doped with dopants of a first dopant type;an emitter layer doped with dopants of a second dopant type;a window layer having a lattice structure matched to the lattice structure of the emitter layer;wherein each one of the plurality of layers comprises a type III-V semiconductor;a beta particle source for generating beta particles; andwherein the substrate comprises a GaAs substrate, the base layer comprises an n type InGaP layer, the emitter layer comprises a p type InGaP layer, and the window layer comprises a p type InAlP layer. 2. The device of claim 1 further comprising an InGaP back surface reflector layer between the substrate and the base layer. 3. The device of claim 1 wherein the plurality of stacked material layers further comprises a GaAs cap layer disposed between the window layer and the beta particle source, wherein a doping level of the cap layer is about 10^18 ND/cm^3. 4. The device of claim 1 further comprising an intrinsic InGaP layer between the base layer and the emitter layer, wherein a thickness of the intrinsic InGaP layer is between about 1000 and 3000 Angstroms or is between about 50 and 100 Angstroms. 5. The device of claim 1 wherein a bandgap of the window layer is greater than the bandgap of the emitter layer. 6. A device for producing electricity, comprising:a substrate;a plurality of stacked material layers above the substrate, the plurality of stacked material layers comprising,a base layer doped with dopants of a first dopant type;an emitter layer doped with dopants of a second dopant type;a window layer having a lattice structure matched to the lattice structure of the emitter layer;wherein each one of the plurality of layers comprises a type III-V semiconductor;a beta particle source for generating beta particles; andwherein the substrate comprises a GaAs substrate, the base layer comprises a p type InGaP layer, the emitter layer comprises an n type InGaP layer, and the window layer comprises an n type InAlP layer. 7. The device of claim 6 further comprising an InGaP back surface reflector layer between the substrate and the base layer. 8. The device of claim 6 wherein the plurality of stacked material layers further comprises a GaAs cap layer disposed between the window layer and the beta particle source, wherein a doping level of the cap layer is about 10^18 ND/cm^3. 9. The device of claim 6 further comprising an intrinsic InGaP layer between the base layer and the emitter layer, wherein a thickness of the intrinsic InGaP layer is between about 1000 and 3000 Angstroms or is between about 50 and 100 Angstroms. 10. The device of claim 6 wherein a bandgap of the window layer is greater than the bandgap of the emitter layer. 11. A multilayer device for producing electricity, comprising:a beta particle source layer for generating beta particles; andat least three semiconductor layers each having a bandgap substantially similar to a band gap of the other layers, the at least three layers comprising a doped emitter top layer, an undoped intermediate layer and a doped bottom base layer, wherein the emitter and the base layers are doped with opposite-type dopants, and wherein the emitter layer is closer to the beta particle source layer than the base layer; wherein the emitter and the intermediate layers absorb more beta particles than the base layer. 12. The device of claim 11 further comprising a window layer in contact with the emitter layer and a cap layer atop the window layer, wherein the window layer is doped with dopants of the same dopant type as the emitter layer, the window layer having a bandgap larger than the bandgap of the emitter, intermediate and base layers, the window layer having a closely matched lattice to the emitter layer, the cap layer for current collection and for protecting the device from environmental effects.