ENGINEERING OF THE NONRADIATIVE TRANSITION RATES IN NONPOLAR MODULATION-DOPED MULTIPLE-QUANTUM WELLS

The feasibility of population inversion, by impurity-scattering enhanc ement of the acoustic-phonon-limited lower-laser-level intersubband re laxation rate, is theoretically investigated in nonpolar three-level S iGe/Si systems. The dependence of the acoustic-phonon depopulating rat e on the barrier thickness and the effect of the position of a delta-d oped region on the impurity scattering are treated rigorously. A 10-An gstrom-doped region with a 10(10) or a 5 x 10(10) cm(-2) sheet carrier density enhances the acoustic-phonon-limited depopulating rate by mor e than one or two orders of magnitude, respectively. Thus for equal ba rrier widths between the depopulating and the lasing levels, the depop ulating rate becomes at least an order of magnitude (10(10) cm(-2) dop ing) or a factor of 2-4 (5 x 10(10) cm(-2) doping) faster than the las ing transition's acoustic- or optical-phonon limit, respectively. This allows for the design of nonpolar intersubband lasers, in which popul ation inversion between discrete valence-band states is achieved by im purity-scattering enhancement of the acoustic-phonon-limited depopulat ing rate. (C) 1997 Optical Society of America.