Intersubband population inversion in quantum wire structures

When the spacing between subbands in a quantum wire is equal to the optic phonon energy a situation occurs under longitudinal field conditions where the upper subband population is enhanced with respect to the lower subband. We focus our investigation on the case where a third, intermediate subband is located slightly below the upper subband. We use a Monte Carlo simulation and obtain a population inversion between the upper and intermediate subbands. Intersubband optical transitions with the possibility of far-infrared stimulated emission seem to be significant.