Optical properties of (001)- and (111)-oriented (In,Ga)As-GaAs strained-layer superlattices

Photoluminescence excitation experiments on a series of nominally identical (In,Ga)As-GaAs multiple-quantum-well samples grown on both (001)- and (111)-oriented GaAs substrates show that the energy position of the fundamental exciton creation peak in the (111) samples is within a few meV of the corresponding one in the (001) samples. We attribute this lack of a significant energy shift to strong screening of the internal piezoelectric field by free carriers supplied principally from the ${\mathit{n}}^{+}$-type GaAs substrate. Additional peaks in the (111) samples suggest that screening, though strong, is incomplete.