Evidence of carrier localization in photoluminescence spectroscopy studies of mid-wavelength infrared InAs/InAs_1−xSb_x type-II superlattices

The temperature-dependent and excitation-dependent photoluminescence (PL) spectroscopy characterization of mid-wavelength infrared InAs/InAs_1−xSb_x type-II superlattices reveals evidence of carrier localization. Carrier localization is apparent in the 8 meV PL peak position blue shift from 4 K to 60 K while the peak full-width-at-half-maximum is non-monotonic, peaking at 25 K before increasing above 60 K. In addition, competition between two recombination processes is evident in the temperature-dependent behavior of the PL peak integrated intensity under low excitation conditions: the intensity decreases from 4 K to 80 K, increases from 80 K to 160 K, and decreases above 160 K. Excitation-dependent PL studies reveal the dominant recombination mechanism changes from free-to-bound or donor–acceptor-like recombination to excitonic or band-to-band recombination at ~60 K. These findings suggest that carrier localization is occurring below 60 K, and the confined carriers are holes as these are unintentionally doped n-type superlattices. The localization potentials are due to variations in the InAs_1−xSb_x composition, the interfaces, and the InAs and InAs_1−xSb_x layer widths. The width of a Gaussian distribution used to describe the density of states of the band tails due to carrier localization potentials ranges from 2 meV–4 meV. The larger energy corresponds to the smaller period superlattices, indicating the interface compositional variation is more prominent and creates larger localization potentials than in the longer period superlattices.