Recombination mechanisms at window/emitter interface in InP and other III-V semiconductor based solar cells

Abstract

The effect of various window layers for InP solar cells are studied. Window materials that have type I and type II alignments in the window/emitter interface are compared. All window materials that form a type II alignment with InP, such as Al/sub 0.20/In/sub 0.80/P, Ga/sub 0.20/In/sub 0.80/P, Al/sub 0.55/In/sub 0.45/As and Al/sub 0.60/In/sub 0.40/P, cause a high interface recombination velocity, which deteriorates the carrier collection. This recombination takes place due to the spatially indirect quantum well transition between the triangular quantum wells formed in the interface. ZnSe as a window layer material with type I alignment does not have this problem, but decreased response in the short wavelength region is observed due to misfit dislocation induced trap sites. Future prospects for the window layer development for InP are discussed. The discussion is extended also to other III-V semiconductor based solar cell materials, such as Ga/sub 0.5/In/sub 0.5/P solar cells with Al/sub x/Ga/sub 1-x/As window layers.