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

Enhanced emission efficiency due to an excited subband resonance in a GaAs-based quantum-well system

“…According to the PLE data, the inner Al 0.2 Ga 0.8 As barriers show variations of the Al mole fraction from 0.22 to 0.16, leading to a 27% reduction from the center to the edge in general agreement to the case of the outer Al 0.3 Ga 0.7 As barriers. Since the reduction of the Al content of the inner Al 0.2 Ga 0.8 As barriers, that is, the decrease of the QW potential depth causes a reduction of the quantum confinement, the observed red-shifts for QW1, QW2, and QW3 are explained in agreement with the calculated transition energies based on the envelope function approximation [11]. Fig.…”

“…The sample used for this study consists of three different QWs grown on a 2-in undoped GaAs (1 0 0) substrate by molecular beam epitaxy (MBE), prepared with growth interruption at the QW interfaces [10][11][12][13][14]. The nominal widths of the GaAs QWs, which are separated from each other by 36 nm thick Al 0.2 Ga 0.8 As inner barriers, amount to 7.8 nm (QW1), 5.5 nm (QW2), and 3.5 nm (QW3) starting from the substrate side.…”

“…Interestingly, the intensity of the IL band is higher than the one of the QW bands and shows its largest value at the spot position near the center of the wafer, but not exactly at the center. It is important to note that the PL intensity of the IL also exhibits a maximum at a position slightly away from the center of the wafer [11]. The use of an electron beam energy of 20 keV, which generates more carriers in the bottom outer barrier, enhances the capture of carriers into the nearest IL [13,14].…”

“…The significant reduction of the corresponding CL intensity can be explained by an efficient carrier capture into the QWs after temporarily residing within the thin inner Al 0.2 Ga 0.8 As barriers. The energy relationship between the lines of the IL and the inner barriers as determined by PL excitation (PLE) spectroscopy [11] allows us to determine the Al content (x) of the inner barriers for the corresponding CL spot positions. Thus, we are able to determine the transition energies of the CL lines as a function of x, as plotted in Fig.…”

“…Compared to the low-energy exciton emission bands originating from the introduced QWs, a surprisingly intense high-energy emission is observed due to an unintentionally introduced interface layer formed in the barrier heterostructure. We discuss a possibility that the high-energy radiative recombination can be significantly enhanced, when it is in resonance with the excited subband transition of a neighboring QW.The sample used for this study consists of three different QWs grown on a 2-in undoped GaAs (1 0 0) substrate by molecular beam epitaxy (MBE), prepared with growth interruption at the QW interfaces [10][11][12][13][14]. The nominal widths of the GaAs QWs, which are separated from each other by 36 nm thick Al 0.2 Ga 0.8 As inner barriers, amount to 7.8 nm (QW1), 5.5 nm (QW2), and 3.5 nm (QW3) starting from the substrate side.…”