NOVELTY - The optoelectronic semiconductor device comprises an absorber layer (108) that is made of a direct bandgap semiconductor and has a type of doping, an emitter layer located closer than the absorber layer to a back side of the device such that single carrier transport is provided in the device, a heterojunction formed between the emitter layer and the absorber layer, a p-n junction formed between the emitter layer and the absorber layer at a specified location offset from the heterojunction, an n-metal contact (105) disposed on a front side of the device, and a p-metal contact (112).    USE - Used as an optoelectronic semiconductor device such as photovoltaic devices including solar cells.    ADVANTAGE - The optoelectronic semiconductor device can be economically and efficiently manufactured with high flexibility and long lifetime.    DETAILED DESCRIPTION - The optoelectronic semiconductor device comprises an absorber layer (108) that is made of a direct bandgap semiconductor and has a type of doping, an emitter layer located closer than the absorber layer to a back side of the device such that single carrier transport is provided in the device, a heterojunction formed between the emitter layer and the absorber layer, a p-n junction formed between the emitter layer and the absorber layer at a specified location offset from the heterojunction, an n-metal contact (105) disposed on a front side of the device, a p-metal contact (112) disposed on a back side of the device, and a dielectric material. The emitter layer is made of a different material than the absorber layer, and has a higher bandgap than the absorber layer. The p-n junction causing a voltage to be generated in the device in response to the device is exposed to light at the front side of the device. The front side is disposed over the back side. The p-metal contact has reflectivity such that light trapping that leads to enhanced photon recycling is enabled and the performance including the open circuit voltage of the device is enhanced, and comprises a stack of metallic layers. One of the metallic layers is highly reflective. The dielectric material is placed between the stack of metallic layers and the backside of the device. The offset of the p-n junction from the heterojunction is provided by an intermediate layer (114) located between the absorber layer and the emitter layer. The intermediate layer has the same type of doping as the absorber layer, and includes the different material, a graded layer (115) having a material gradation made of gallium arsenide at a side closer to the absorber layer, and a back window layer (117) having an uniform composition of the material. The graded layer is located adjacent to the absorber layer. The back window layer is located between the graded layer and the emitter layer.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic cross-sectional view of a photovoltaic unit.    N-type contact layer (105)    N-type absorber layer (108)    P-type contact layer (112)    Intermediate layer (114)    Graded layer (115)    Back window layer. (117)