Low-threshold intersubband laser based on interface-scattering-rate engineering

The dependence of the scattering rate between different electronic states in semiconductor heterostructures due to interface roughness on the barrier height is exploited to enhance the population inversion in intersubband lasers. Barriers with differing heights are used within a strain-compensated InGaAs-InAlAs heterostructure to either increase or decrease the interface-roughness scattering component for specific confined states. In particular, low barriers are used where the upper laser state has its highest probability, thus maximizing the lifetime of the upper laser state; the higher barriers are used where the lower laser state and the few subsequent confined states have their highest probabilities, thus minimizing the lifetime of the lower laser state. By combining differing barrier heights in this way, the lifetime of the upper laser state is increased, while simultaneously the lifetime of the lower laser state is decreased; thus, the population inversion is significantly enhanced. This design approach is demonstrated for a quantum-cascade laser emitting near 4 mu m. The reduced scattering out of the upper laser level is reflected in a narrower electroluminescence spectrum of 26 meV and a reduced threshold current density of 1.75 kA/cm(2) at room-temperature. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3701824]