NOVELTY - The semiconductor structure (200) such as a solar cell or a photovoltaic cell useful in multi-color light emitting devices and photodetectors, comprises a III-V or II-VI substrate (201), six multi-junction building blocks (202, 203, 204) formed over the substrate, a tunnel junction between each of the multi-junction building blocks, and a buffer layer between the substrate and the first multi-junction building block. Each multi-junction building block independently comprises a p-n junction having two III-V or II-VI alloy layers (202a, 202b, 203a, 203b, 204a, 204b).    USE - The semiconductor structure such as a solar cell or a photovoltaic cell is useful for terrestrial and space applications, and in multi-color light emitting devices and photodetectors.    ADVANTAGE - The semiconductor structure has higher energy conversion efficiency, high-quality near-lattice-matched materials with the optimally spaced bandgaps and increased open circuit voltage thus lowering the overall cost for electricity generation.    DETAILED DESCRIPTION - The semiconductor structure (200) such as a solar cell or a photovoltaic cell useful in multi-color light emitting devices and photodetectors, comprises a III-V or II-VI substrate (201), six multi-junction building blocks (202, 203, 204) formed over the substrate, a tunnel junction between each of the multi-junction building blocks, and a buffer layer between the substrate and the first multi-junction building block. Each multi-junction building block independently comprises a p-n junction having two III-V or II-VI alloy layers (202a, 202b, 203a, 203b, 204a, 204b), in which one alloy layer is p-doped and the other is n-doped, P or p+ doped third layer and N or n+ doped fourth layer, and has a bandgap energy of 2-2.5 eV. The multi-junction building blocks are lattice matched or pseudomorphically strained to the substrate. The third and fourth layers comprise the same or a different alloy as the p-n junction. An INDEPENDENT CLAIM is included for a method for preparing a semiconductor structure.    DESCRIPTION OF DRAWING(S) - The figure shows a semiconductor structure.    Semiconductor structure (200)    Substrate (201)    Multi-junction building blocks (202, 203, 204)    Alloy layers. (202a, 202b, 203a, 203b, 204a, 204b)