Negative intersubband absorption in biased tunnel-coupledwells

摘要

We investigate the use of intersubband transitions between two weakly coupledshallow quantum wells to generate or detect terahertz radiation. The wells are dopedfor independent contacting and biasing. The maximum gain (absorption) scales with thewavefunction overlap and difference between the well carrier densities. The absorptionlineshape is studied taking into account the interplay between inhomogeneous andhomogeneous mechanisms of broadening, including both large-scale variations in the coupledlevels and also short-range scattering. The intersubband transitions are strongly renormaliseddue to Coulomb interaction (depolarization and exchange effects). Population inversion canbe achieved through independent variation of the upper and lower well Fermi energy withapplied bias. Numerical estimates of the negative absorption coefficient are obtained usingrealistic parameters, indicating the possible application of such a THz resonator to achievestimulated emission.