Interface-roughness-induced broadening of intersubband electroluminescence in $p$-SiGe and $n$-GaInAs∕AlInAs quantum-cascade structures

The effect of intrasubband interface roughness scattering on intersubband transition linewidths in double-quantum-well and quantum-cascade (QC) structures is studied. In $n$-GaInAs∕AlInAs structures, the calculated ratios between the linewidths of the spatially vertical and diagonal transitions agree with the experimental values. In $p$-Si∕$Si0.2Ge0.8$ QC structures, the experimentally observed linewidth is a factor of 4–7 smaller than the predicted value. However, by assuming a vertical interface correlation between adjacent interfaces separated by less than $∼1.5nm$⁠, the theory reproduces the experiment. Transmission electron microscopy of the SiGe QC sample reveals this vertical correlation, supporting the model.