NOVELTY - The semiconductor material comprises a group IV semiconductor material layer, where the material is not silicon, a first group III-V semiconductor material layer (3) formed of group III atoms and group V atoms and provided with an interface (8) with the group IV semiconductor layer, a first silicon layer (6) formed at the interface between the first group III-V semiconductor layer and the group IV semiconductor layer or formed in the group IV semiconductor layer or the first group III-V semiconductor layer spaced from the interface, and an n-type group V doped region (4).    USE - The semiconductor material is useful in a light absorbing cell of a multi-junction photovoltaic device such as solar cell (all claimed).    ADVANTAGE - The semiconductor material improves efficiency and performance of the lightweight solar cell.    DETAILED DESCRIPTION - The semiconductor material comprises a group IV semiconductor material layer, where the material is not silicon, a first group III-V semiconductor material layer (3) formed of group III atoms and group V atoms and provided with an interface (8) with the group IV semiconductor layer, a first silicon layer (6) formed at the interface between the first group III-V semiconductor layer and the group IV semiconductor layer or formed in the group IV semiconductor layer or the first group III-V semiconductor layer spaced from the interface, and an n-type group V doped region (4) formed in the group IV semiconductor layer that has a border with the interface and is doped by the group V atoms forming the first group III-V semiconductor layer. A part of the n-type group V doped region in the group IV semiconductor layer that is positioned on a side of the silicon layer is doped by the group V atoms of forming a part of the first group III-V semiconductor that is positioned on an opposite side of the silicon layer. Some of the group V atoms doping the part of the group IV semiconductor layer that is positioned on the side of the silicon layer are from the part of the first group III-V layer that is positioned on the opposite side of the silicon layer. The group V doped region in the semiconductor layer provides a p-n junction (2) with a p-type region in the group IV semiconductor layer. The group V doped region in the group IV semiconductor layer and the first group III-V semiconductor layer form a tunnel diode at the interface. The first group III-V semiconductor material at the interface is p-doped and n-type. The group IV semiconductor layer comprises an epitaxial group IV semiconductor layer between the silicon layer and the first group III-V semiconductor layer. The first group III-V semiconductor layer comprises an epitaxial group III-V semiconductor layer between the silicon layer and the group IV semiconductor layer. The group IV semiconductor layer comprises a substrate layer and an epitaxial layer grown on the substrate layer. The silicon layer has a thickness of less than or equal to 7.5 Angstrom , and is less than or equal to 1 atomic layer. A concentration of the doping of the first group III-V semiconductor layer bordering the interface is greater than 1-5x 1018 atoms per cm3. A concentration of the group V atoms of the doping of the n-type group V doped region in the group IV semiconductor layer is greater than 6x 1018 atoms per cm3. A doping concentration of the group IV layer not doped by the group V atoms is between 1x 1017-1x 1018 atoms per cm3. The semiconductor material further comprises a second group III-V semiconductor material layer having an interface with the group IV semiconductor layer at the opposite side of the group IV layer to the interface with the first group III-V semiconductor layer and a second silicon layer at the interface between the second III-V semiconductor layer and the group IV layer. INDEPENDENT CLAIMS are included for:    (1) a multi-junction photovoltaic device;    (2) a method for manufacturing a semiconductor material; and    (3) a method for making a multi-junction photovoltaic device.    DESCRIPTION OF DRAWING(S) - The figure 2 shows a schematic cross-sectional view of semiconductor layers of a lower cell of a multi- junction photovoltaic device, and the figure 11 shows a schematic perspective view of a multi- junction photovoltaic device.    P-n junction (2)    Group III-V semiconductor material layer (3)    N-type group V doped region (4)    Silicon layer (6)    Interface (8)    Light absorbing layers. (111, 112)