Decreasing the emission wavelength of GaAs–AlGaAs quantum cascade lasers by the incorporation of ultrathin InGaAs layers

Abstract

We demonstrate that the emission wavelength of GaAs–Al0.33Ga0.67As quantum cascade lasers can be decreased significantly by incorporating InGaAs layers within the active regions. InAs monolayers are deposited during growth, with segregation effects resulting in the formation of thin InGaAs layers within the GaAs active region quantum wells of the laser. The InGaAs layers are positioned close to the antinodes of the lower laser level wave function, thus decreasing its confinement energy. The small spatial overlap of the InGaAs layers with the upper laser level minimizes the perturbation of the upper state. Consequently, the energy separation between the upper and lower laser levels increases, reducing the emission wavelength. The measured operating wavelength of 7.4 μm is the shortest reported for a GaAs–AlGaAs quantum cascade laser and is approximately 2 μm less than for an identical structure without InGaAs layers in the active regions.