The feasibility of population inversion, by impurity-scattering enhancement of the acoustic-phonon-limited lower-laser-level intersubband relaxation rate, is theoretically investigated in nonpolar three-level SiGe/Si systems. The dependence of the acoustic-phonon depopulating rate on the barrier thickness and the effect of the position of a δ-doped region on the impurity scattering are treated rigorously. A 10-Å-doped region with a or a sheet carrier density enhances the acoustic-phonon-limited depopulating rate by more than one or two orders of magnitude, respectively. Thus for equal barrier widths between the depopulating and the lasing levels, the depopulating rate becomes at least an order of magnitude ( doping) or a factor of 2–4 ( doping) faster than the lasing transition's acoustic- or optical-phonon limit, respectively. This allows for the design of nonpolar intersubband lasers, in which population inversion between discrete valence-band states is achieved by impurity-scattering enhancement of the acoustic-phonon-limited depopulating rate.
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