GaAlAs Allox/Pseudoalloy Type II Structures

The existence of type-II structures made from the combination of Ga$\text{}_{1-x}$AI$\text{}_{x}$As alloy and a short period GaAs/AlAs type-I superlattice is presented. Such three material structures are of type-II having at the same time electrons and holes of Γ-symmetry. This contrasts with the usual situation in type-II two material GaAs/AlAs structure where the ground state of electrons is of X-symmetry. The mechanism allowing creation of three material type-II structures is based on the difference of effective masses of electrons and holes. It should be valid for all similar semiconductor systems. Experimental results of photoluminescence and photoluminescence excitation studies of such structures made by Molecular Beam Epitaxy are presented. We determine the mutual positions of the electron and hole ground levels in the alloy and pseudoalloy and confirm that the studied structure is of type-II.