Simultaneous lasing of interband and intersubband transitions in InAsAlSb quantum cascade laser structures

We show that both interband and intersubband transitions in n-InAsAlSb quantum cascade laser structures can have sufficient gain to enable simultaneous lasing at the two transitions. High electric fields generate holes, which are necessary for interband lasing in InAs. The doping concentration in the injection parts is shown to be critical for controlling the electric fields in the device, enabling the selection of lasing at the intersubband transition alone (high doping), at the interband transition alone (low doping), and simultaneous lasing at both transitions (intermediate doping).