Intersubband staircase laser

A quantum-cascade laser is presented in which the injection minibands are omitted. The intersubband laser operates as a four-level staircase and has potential for higher gain devices due to an increased confinement factor compared to conventional quantum-cascade lasers. A high threshold current density of 5.9 kA/cm² with peak output powers of 230 mW at 77 K is observed. A large wavelength shift from 9.3 to 10 μm and broadband emission are observed at higher bias fields. This modification to existing quantum-cascade laser designs has potential for higher gain devices, but problems with thermal backfilling and doping limit the operating temperature currently to 200 K.