Negative intersubband absorption in biased tunnel-coupled wells

We investigate the use of intersubband transitions between two weakly coupled shallow quantum wells to generate terahertz radiation. The wells are designed for independent contacting and biasing. The maximum gain (absorption) scales with the wavefunction overlap and difference between the well carrier densities. The absorption line shape is studied taking into account the interplay between inhomogeneous and homogeneous broadening mechanisms, including both large-scale variations in the coupled levels and also short-range scattering. The intersubband transitions are strongly renormalized due to Coulomb interactions (depolarization and exchange effects). Population inversion can be achieved through independent variation of the upper and lower well Fermi energy with applied bias. Numerical estimates of the negative absorption coefficient are obtained using realistic parameters, indicating the possible application of such a THz resonator to achieve stimulated emission.