of further illustration fig2 a is a schematic cross section in greater detail of a gainnassb subcell 12 according to the invention the low sb enhanced in and n gainnassb subcell 12 is therefore characterized by its use of low sb enhanced in and n gainnassb as the base layer 220 in the subcell 12 other components of the gainnassb subcell 12 including an emitter 26 an optional front surface field 28 and back surface field 30 are preferably iii v alloys including by way of example gainnas sb in al gaas al ingap or ge the low sb enhanced in and n gainnassb base 220 may either be p type or n type with an emitter 26 of the opposite type to determine the effect of sb on enhanced in and n gainnassb subcell performance various subcells of the type 12 of the structure shown in fig2 b were investigated fig2 b is a representative example of the more general structure 12 in fig2 a base layers 220 with no sb low sb 0 001 u2266 z u2266 0 03 and high sb 0 03 lt z lt 0 06 were grown by molecular beam epitaxy and were substantially lattice matched to a gaas substrate not shown these alloy compositions were verified by secondary ion mass spectroscopy the subcells 12 were subjected to a thermal anneal processed with generally known solar cell processing and then measured under the am1 5d spectrum 1 sun below a filter that blocked all light above the gaas band gap this filter was appropriate because a gainnassb subcell 12 is typically beneath an in gaas subcell in a multijunction stack e g fig1 a and 1b and thus light of higher energies will not reach the subcell 12 fig3.