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(a) FTPL spectra (measured at 10 K) of the D-in-WELL and D-on-WELL structure, respectively. The FTPL peak of the D-in-WELL structure is redshifted by 60 meV compared to the D-on-WELL. (b) FTPLE measurements revealing excited energy levels in the QDs (peak I) and in the QW (peaks II and III). The arrows indicate the centers of the detection energy intervals of the six individual FTPLE spectra for the D-on-WELL (the three uppermost spectra) and the D-in-WELL (the three lower spectra). Peak IV corresponds to the GaAs band edge transition. (c) Schematic pictures of the interband transitions corresponding to the peaks I–IV in the FTPLE spectra.
(a) Photoresponse of the D-in-WELL, which is successively tuned from 120 meV to 148 meV when changing the magnitude and polarity of the applied bias at a temperature of 77 K. The spectra have been normalized to facilitate comparison of the detection energies. (b) Conduction band energy level scheme derived from the interband measurements (c) The tuning possibility is explained by the asymmetric structure, which allows altering of the separation between the QD and the QW states with different applied biases.
(a) Photoresponse of the D-on-WELL, which is tuned from 230 meV to 155 meV when changing the applied bias from 0.9 V to 1.1 V at a temperature of 77 K. (b) Conduction band energy level scheme derived from the interband measurements. Two different intersubband transitions (i and ii) are alternatively dominating the photocurrent spectra, as indicated in (b).
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