TECHNOLOGY FOCUS - MECHANICAL ENGINEERING - Preferred Solar Cell: The multijunction solar cell further comprises: an additional layer of the first p/n type semiconductor material between the delta-doped layer and the second layer. The delta-doped layer having a similar p/n type doping as the second complementary p/n type semiconductor material. The multijunction solar cell further comprises: an additional layer of the second complementary p/n type semiconductor material between the first layer and the delta-doped layer; a substrate; a first photovoltaic subcell grown epitaxially on the substrate; and a second photovoltaic subcell grown epitaxially on the second layer of the tunnel diode; and where the first layer of the tunnel diode is grown on the first photovoltaic subcell. The multijunction solar cell also comprises: a set ofphotovoltaic subcells, each of the set of photovoltaic subcells separated by a tunnel diode having a delta-doped layer. The dopant concentration in the delta doped layer is approximately 10 times greater than the dopant concentration of the first layer. The dopant concentration of delta doped layer is greater than 1020 cm3. The width of the delta doped layer is approximately 20 Angstroms. The first photovoltaic subcell comprises a semiconductor material having a bandgap lower than the second photovoltaic subcell. The first photovoltaic subcell comprises Gallium Indium Arsenide and the second photovoltaic subcell comprises Gallium Indium Phosphide. The tunnel diode comprises a material having a bandgap equal to or higher than the first photovoltaic cell. The tunnel diode comprises a semiconductor material selected from the group consisting of Gallium Arsenide, Gallium Indium Arsenide, Gallium Indium Phosphide, and Aluminum Gallium Arsenide. The first photovoltaic subcell and the second photovoltaic subcell are n-on-p subcells; and where the first layer and the delta-doped layer are a Group II, IV or V n-type doped semiconductor material, and the second layer is a Group IV or VI p-type doped semiconductor material. Alternatively, the multijunction solar cell having an interconnection tunnel junction with a delta-doped layer prepared by a process comprising: (a) preparing a substrate; (b) growing epitaxially a first photovoltaic subcell on the substrate; (c) growing epitaxially a first layer of a tunnel diode on the first photovoltaic subcell, the first layer using a dopant of an acceptor/donor type of an adjoining portion of the first photovoltaic subcell; (d) interrupting the step of growing epitaxially the first layer of the tunnel diode; (e) depositing a delta-doped layer of a delta dopant of same acceptor/donor type as the dopant on the first layer of the tunnel diode, the delta dopant in the delta-doped layer reaching a delta dopant concentration substantially greater than a concentration of the dopant in the first layer of the tunnel diode; and (f) growing epitaxially a second layer of the tunnel diode on the delta-doped layer, the second layer using a complementary dopant of a different acceptor/donor type to the dopant of the first layer of the tunnel diode. The process further comprises: (g) growing epitaxially an additional portion of the first layer using the dopant, after the step (e) depositing the delta-doped layer and before the step (f) growing epitaxially the second layer, where steps (e) is: (e) depositing a delta-doped layer of a delta dopant of same acceptor/donor type as the complementary dopant on the first layer of the tunnel diode, the delta dopant in the delta-doped layer reaching a delta dopant concentration substantially greater than a concentration of the complementary dopant in the second layer of the tunnel diode. The steps (d), (e), and (f) are: (d) growing epitaxially a second layer of the tunnel diode on the first layer of the tunnel diode, the second layer using a complementary dopant of a different acceptor/ donor type to the dopant of the first layer of the tunnel diode; (e) interrupting the step of growing epitaxially the second layer of the tunnel diode; and (f) depositing a delta-doped layer of a delta dopant of same acceptor/donor type as the complementary dopant on the second layer of the tunnel diode, the delta dopant in the delta-doped layer reaching a delta dopant concentration substantially greater than a concentration of the complementary dopant in the second layer of the tunnel diode. Preferred Method: Manufacturing a delta-doped interconnection tunnel junction further comprises: growing epitaxially an additional layer using the first dopant, after the depositing step; preparing a substrate; growing epitaxially a first photovoltaic subcell; and growing epitaxially a second photovoltaic subcell; and where the first photovoltaic subcells is grown on the substrate, the first layer of the tunnel diode is grown on the first photovoltaic subcell, and the second photovoltaic subcell is grown on the second layer of the tunnel diode. The first photovoltaic subcell comprises a material having a bandgap lower than the second photovoltaic subcell. The tunnel diode comprises a material having a bandgap equal to or higher than the first photovoltaic cell.