Abstract: A photovolatic device is disclosed comprising a p-type conductive substrate, a sandwich of p-type Al.sub.y Ga.sub.(1-y) As bottom layer/p-type GaAs base layer/p-type Al.sub.y Ga.sub.(1-y) As top layer (wherein the surface area of the p-type Al.sub.y Ga.sub.(1-y) As top layer is less than the surface area of the p-type GaAs base layer, a layer of n.sup.+ -type GaAs emitter contacting the surface of the p-type GaAs base layer (wherein the surface area of the layer of n.sup.+ -type GaAs emitter is less than one-tenth the surface area of the p-type GaAs base layer), an insulating layer contacting the surface of the p-type Al.sub.y Ga.sub.(1-y) As top layer, and means for forming electrical contacts to the substrate and the incident surface of the n.sup.+ -type GaAsemitter layer.