NOVELTY - The semiconductor device e.g. solar or photovoltaic cell (10) has emitter layers (22,42,62) in electrical connectivity with the base layers e.g. gallium indium phosphide base layer (24), gallium (indium) arsenide base layer (44) and germanium base layer (64). The base layers and emitter layers form a p-n junction in the solar or photovoltaic cell or other optoelectronic device. A low bandgap absorber region is set in either or both of the base layer and emitter layer.    USE - Lattice mismatched or metamorphic semiconductor device e.g. solar cell, subcell or optoelectronic device for converting sunlight into electrical energy by photovoltaic effect.    ADVANTAGE - Provides solar cells and other optoelectronic devices having increased photogenerated current density in given solar spectrum. Increases photogeneration of charge carriers in solar cells and other optoelectronic devices, particularly for devices that rely weakly absorbing layers due to other design constraints. Minimizes absorption of photons by mechanisms that do not result in useful current in order to reduce solar cell temperature under normal operating conditions. Increases energy conversion efficiency of multijunction solar cell. Enables tuning of effective bandgap of one or more subcells in multijunction solar cell while maintaining given lattice constant in metamorphic subcell. Improves match of the subcell effective bandgap combination to that of the solar spectrum and as well as improve the solar cell efficiency. Reduces thermal load on cell under operating conditions, and as well as improves tolerance for ionizing radiation environments.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for a method for forming semiconductor device.    DESCRIPTION OF DRAWING(S) - The drawing shows the isometric drawing of the 3-junction, metamorphic solar.    Solar or photovoltaic cell (10)    Emitter layers (22,42,62)    Gallium indium phosphide base layer (24)    Gallium indium arsenide base layer (44)    Germanium base layer (64)