A dual-color injection laser based on intra- and inter-band carrier transitions in semiconductor quantum wells or quantum dots

A new type of semiconductor injection laser capable of simultaneously gener ating radiation in the mid-infrared (MIR) (lambda similar to 10 mum) and ne ar-infrared (NIR) (lambda similar to 0.9 mum) spectral regions is proposed. The MIR emission is a result of intersubband (intraband) electron transiti ons within a three-level conduction band in a quantum well or a quantum dot . The NIR emission, on the other hand, is due to conventional interband rec ombination of injected electrons and holes into the conduction and valence bands, respectively. The conditions for population inversion in the intersu bband emission process are determined by an appropriately engineered energy structure for a three-level system in the conduction band of a quantum wel l or dot structure; for the quantum-well-based system, the structure has an asymmetric funnel shape to provide long electron-phonon lifetime at the th ird (top) energy level. Under high carrier injection, NIR interband emissio n depopulates the conduction ground level of the quantum well, thereby stab ilizing the electron concentration at this level-a necessary condition for the operation of the MIR laser. This paper discusses the calculation of the population inversion conditions, the requisite gain, and threshold current for the MIR laser operation. We also present a preliminary design of the l aser structure with a composite waveguide that accommodates both mid- and N IR stimulated emission.