Inversion of electron sub-band population in a GaAs/AlGaAs triple barrier tunnelling structure

Abstract We have used interband photoluminescence (PL) spectroscopy to demonstrate the occurrence of an intersubband population inversion in a GaAs/AlGaAs triple barrier structure containing asymmetric coupled quantum wells. The relative populations of the n =1 ( E 1 ) and n =2 ( E 2 ) electron subbands of the wider quantum well (QW1) are deduced from the relative intensities of the PL peaks arising from recombination of the E 1 and E 2 electrons. A significant population inversion is obtained between E 2 and E 1 when the structure is biased so that E 1 is in resonance with the n =1 ( E 1 *) level of the narrower quantum well (QW2). The data indicate a zone-centre population ratio of n 2 / n 1 ≈40 at the E 1 – E 1 * resonance bias. We show that this corresponds to an overall population ratio of n 2 / n 1 ≈5, consistent with the predictions of rate equation analysis.