| Recently, an entirely new class of optical devices has been proposed based on interference between intersubband transitions in quantum wells. These infrared devices include an intersubband laser that operates without a population inversion, and efficient non-linear optical elements, which rely on a destructive interference between intersubband transitions to sharply reduce the rate of absorption. Scattering events, which can dephase electrons in the double quantum well structure, can wash out the interference effects central to device operation. It is the purpose of the present research to gain an understanding of scattering processes in quantum wells, and to use that understanding to fabricate a double quantum well structure for the observation of quantum interference effects.; Initial experiments focused on the linewidth of intersubband transitions in single, GaAs quantum wells. From the dependence of the linewidth on the width of the quantum well, we have determined that interface roughness scattering is the predominant broadening mechanism. Additional experiments have shown that alloy-disorder scattering, which has a strong, adverse effect on Hall mobility, does not broaden an intersubband transition. Using this information to minimize scattering rates, we have fabricated a double quantum well structure coupled to a continuum of states by a thin tunneling barrier. Under conditions in which the ground state of the alloyed, AlGaAs quantum well is resonant in energy with the first excited state of the GaAs quantum well, we have observed destructive interference effects in the intersubband absorption spectrum. At certain energies, the absorption is reduced by as much as two-thirds compared to a situation without interference. This phenomenon can be termed resonant tunneling induced transparency, in direct analogy to the electromagnetically induced transparency observed in atomic systems. |
