Abstract: Zinc diffusion procedures applicable for large scale manufacture of GaAs and GaSb cells used in tandem solar cells having a high energy conversion efficiency. The zinc doping and carrier concentration are restricted to be less than about 10.sup.19 /cm.sup.3 to obtain good light generated carrier collection and hence good short circuit currents. The amount of zinc that is available for diffusion during a drive-in heating step is restricted. Confinement of zinc and arsenic vapors during the heating step may be effected by use of a proximity source wafer or by an encapsulant layer. The zinc diffusion of GaSb is obtained by a homogeneous light diffusion that is followed by a patterned heavy diffusion to give low ohmic contact with the grid lines. Texture etching of the GaSb solar cell is also compatible with this diffusion process.