Strong photoluminescence emission from an excited-subband exciton state in a GaAs/AlxGa1−xAs triple quantum well with different well thicknesses

We have studied the photoluminescence (PL) properties of a GaAs/AlxGa1−xAs quantum well (QW) system containing three QWs with different thicknesses, in which the widest one View the MathML source has an excited-subband exciton state located slightly below the barrier band edge. Using above-barrier excitation with a power density of about View the MathML source at View the MathML source, a strong PL emission peak appears on the high-energy side of the three PL peaks originating from the ground-state exciton transitions of the three QWs. This high-energy PL peak with an intensity comparable to the one of the other three peaks is located near an excited-subband (n=2) exciton state of the widest QW. By investigating the position dependence of the PL spectra across a 2-inch wafer, which exhibits a decreasing Al mole fraction x from the center to the edge, the PL intensity of the high-energy peak can be correlated with the one of the ground state in the widest QW. This correlation indicates that this high-energy PL peak is most likely related to the n=2 exciton state of the widest QW because of the energy alignment of the excited subband state relative to the barrier band edge.