Demonstration of a blueshift in type II asymmetric InP/InAsP/InGaAs multiple quantum wells

Room temperature photocurrent measurements were carried out on two InAsxP1−x/In0.53Ga0.47 As asymmetric quantum wells with InP barriers, grown by molecular beam epitaxy. The lowest energy exciton transition in these samples was close to 1.5 μm. A significant blueshift of this transition was observed on application of an electric field. We attribute this blueshift to the type II band lineup that exists between InAsP and InGaAs for the samples studied. The resulting stepped well causes separation of the electron and hole wave functions at zero bias, which is then reduced by the applied field. X-ray diffraction spectra indicated layer thicknesses and compositions to be close to the intended values. However, to fit the observed transition energies, spectral shifts, and x-ray data simultaneously, it was necessary to assume low levels of arsenic contamination in the InP barriers and of gallium in the InAsP layers. From these results, we infer the maximum value of the conduction band offset (ΔEc) for InAsP/InP to be approximately 65% of the band-gap difference (ΔEg).