High-performance quantum cascade lasers with electric-field-free undoped superlattice

An optimized design of quantum cascade lasers with electric field free undoped superlattice active regions is presented. In these structures the superlattice is engineered so that: (1) the first two extended states of the upper miniband are separated by an optical phonon to avoid phonon bottleneck effects and concentrate the injected electron density in the lower state and (2) the oscillator strength of the laser transition is maximized. The injectors' doping profile is also optimized by concentrating the doping in a single quantum well to reduce the electron density in the active material. These design changes result in major improvements of the pulse/continuous-wave performance such as a weak temperature dependence of threshold (T
₀
=167 K), high peak powers (100-200 mW at 300 K) and higher CW operating temperatures for devices emitting around at /spl lambda//spl sim/8.5 μm.