Non-cascaded intersubband injection lasers and scaling with the number of stages in quantum cascade lasers

Summary form only given. One key feature of quantum cascade (QC) lasers is the cascading scheme: typically N/spl ap/25 periods of alternated active regions and electron injectors form a common active waveguide core which increases the optical confinement and therefore the modal gain sufficiently to overcome the increased waveguide losses at mid-infrared (3-13 /spl mu/m) wavelengths. Consequently, the cascading scheme results in comparatively low threshold current densities, as well as in an inherently high optical output power as each electron above laser threshold creates photons in all N stages which it successively traverses. The rapid progress and high performance of QC-lasers strongly reinforced the notion that cascading is essential for intersubband injection lasers. We demonstrate the first non-cascaded intersubband injection lasers based on a single active region. Several major advantages arise from this new structure: first, only few layers are necessary to build the active region core, which simplifies sample growth and preparation. Second, low operating voltages /spl sim/2-3 V are achieved, which is essential for applications which have previously been optimized for interband diode lasers and their low voltage compliance requirements. The laser structure has been grown in the InGaAs/AlInAs on InP material system using molecular beam epitaxy.