A multijunction solar cell, comprising: a first layer of a tunnel diode of a first p or n type semiconductor material; a delta-doped layer (404, 502) having a similar p or n type doping as said first p or n type semiconductor material, wherein when the first p or n type semiconductor material has an n type doping the delta-doped layer has an n type doping and when the first p or n type semiconductor material has a p type doping the delta-doped layer has a p type doping, said delta-doped layer (404, 502) substantially thinner than said first layer, said delta-doped layer (404, 502) reaching a dopant concentration substantially higher than a dopant concentration of said first layer, and said delta-doped layer (404, 502) contacts said first layer; a second layer of said tunnel diode of a second complementary p or n type semiconductor material to said first layer of said tunnel diode and said delta-doped layer (404, 502), wherein said second layer contacts said delta-doped layer (404, 502); a substrate; and a first photovoltaic subcell and a second photovoltaic subcell, wherein the photovoltaic subcells (102, 104) are electrically connected by said tunnel diode, wherein the first photovoltaic subcell contacts the substrate, the second photovoltaic subcell contacts the second layer of the tunnel diode, and the first layer of the tunnel diode contacts the first photovoltaic subcell; wherein the delta-doped layer (404, 502) is directly adjacent to the second layer; wherein adjacent portions of the tunnel diode and the photovoltaic subcells (102, 104) have the same p or n type doping; wherein the first photovoltaic subcell comprises an n-type doped layer of Gallium Indium Arsenide and a p-type doped layer of Gallium Indium Arsenide and the second photovoltaic subcell comprises an n-type doped layer of Gallium Indium Phosphide and a p-type doped layer of Gallium Indium Phosphide; wherein the first layer of the tunnel diode comprises Gallium Indium Arsenide and the second layer of the tunnel diode comprises Gallium Indium Arsenide; and wherein the first layer of the tunnel diode contacts the n-type doped layer of Gallium Indium Arsenide of the first photovoltaic cell and the second layer of the tunnel diode contacts the p-type doped layer of Gallium Indium Phosphide of the second photovoltaic cell; or wherein the first layer of the tunnel diode contacts the p-type doped layer of Gallium Indium Arsenide of the first photovoltaic cell and the second layer of the tunnel diode contacts the n-type doped layer of Gallium Indium Phosphide of the second photovoltaic cell. a first layer of a tunnel diode of a first p or n type semiconductor material; a delta-doped layer (404, 502) having a similar p or n type doping as said first p or n type semiconductor material, wherein when the first p or n type semiconductor material has an n type doping the delta-doped layer has an n type doping and when the first p or n type semiconductor material has a p type doping the delta-doped layer has a p type doping, said delta-doped layer (404, 502) substantially thinner than said first layer, said delta-doped layer (404, 502) reaching a dopant concentration substantially higher than a dopant concentration of said first layer, and said delta-doped layer (404, 502) contacts said first layer; a second layer of said tunnel diode of a second complementary p or n type semiconductor material to said first layer of said tunnel diode and said delta-doped layer (404, 502), wherein said second layer contacts said delta-doped layer (404, 502); a substrate; and a first photovoltaic subcell and a second photovoltaic subcell, wherein the photovoltaic subcells (102, 104) are electrically connected by said tunnel diode, wherein the first photovoltaic subcell contacts the substrate, the second photovoltaic subcell contacts the second layer of the tunnel diode, and the first layer of the tunnel diode contacts the first photovoltaic subcell; wherein the delta-doped layer (404, 502) is directly adjacent to the second layer; wherein adjacent portions of the tunnel diode and the photovoltaic subcells (102, 104) have the same p or n type doping; wherein the first photovoltaic subcell comprises an n-type doped layer of Gallium Indium Arsenide and a p-type doped layer of Gallium Indium Arsenide and the second photovoltaic subcell comprises an n-type doped layer of Gallium Indium Phosphide and a p-type doped layer of Gallium Indium Phosphide; wherein the first layer of the tunnel diode comprises Gallium Indium Arsenide and the second layer of the tunnel diode comprises Gallium Indium Arsenide; and wherein the first layer of the tunnel diode contacts the n-type doped layer of Gallium Indium Arsenide of the first photovoltaic cell and the second layer of the tunnel diode contacts the p-type doped layer of Gallium Indium Phosphide of the second photovoltaic cell; or wherein the first layer of the tunnel diode contacts the p-type doped layer of Gallium Indium Arsenide of the first photovoltaic cell and the second layer of the tunnel diode contacts the n-type doped layer of Gallium Indium Phosphide of the second photovoltaic cell.