Gain without inversion in interband transitions of semiconductor quantum wells from a single-particle perspective

The quantum interferences arising in three-level atomic systems are investigated in analogous asymmetric semiconductor quantum well structures. These investigations lead to the conditions necessary for induced zero absorption and gain without population inversion in interband transitions. Asymmetric quantum well configurations are proposed and analyzed for induced zero absorption and gain without inversion using a single-particle density-matrix approach. This density-matrix approach is described and shown to give the steady-state solutions for absorption and gain without the approximations required for perturbative or iterative methods. Both excitonic and continuum transitions are examined using typical semiconductor parameters with excitonic transitions contributing the largest fraction of gain without inversion. While interband transitions differ from intraband and atomic transitions, results for the proposed quantum well configurations validate the basic concept of inversionless gain in semiconductors and point the way to ultralow threshold semiconductor microlasers. © 1996 The American Physical Society.