Photoluminescence spectroscopy of intersubband population inversion in a GaAs/AlxGa1-xAs triple-barrier tunneling structure

We have used interband photoluminescence (PL) spectroscopy to demonstrate the occurrence of an inter-subband population inversion in a GaAs/AlxGa1-xAs triple barrier structure containing asymmetric coupled quantum wells. The relative populations of the n=1 (EI) and n=2 (E2) electron subbands of the wider quantum well (QW1) are deduced from the relative intensities of the PL peaks arising from recombination of the El and E2 electrons. A significant population inversion is obtained between E2 and EI when the structure is biased so that El is in resonance with the n = I (E1*) level of the narrower quantum well (QW2). The key importance of the interwell resonance in achieving population inversion is confirmed by comparison with PL results from structures in which E1-E1* alignment does not occur.