Short-wavelength intersubband staircase lasers, with and without AlAs-blocking barriers

We present short-wavelength Ga 0.322 In 0.678 As/Al 0.635 In 0.365 As quantum-cascade lasers without injector regions (staircase lasers), with and without AlAs-blocking barriers, emitting at ∼4.55 µm and ∼4.2 µm, respectively. By introducing AlAs-barriers into the active region, a thermally activated escape of electrons from the upper laser state into the quasicontinuum is avoided. The sample without AlAs-barriers shows a maximum operating temperature of 220 K with a threshold current density of 4.3 kA cm −2 . A sample with an improved design with AlAs-blocking barriers shows threshold current densities of 2.9 kA cm −2 at 220 K and 4.8 kA cm −2 at 300 K. The maximum operating temperature has been increased to 370 K.