Abstract
We report two novel methods for reducing the emission wavelength of GaAs–AlAs quantum cascade lasers. We demonstrate that for lasing to occur electron injection into the upper laser level must proceed via Γ states confined below the lowest X state in the injection barrier. The limit this places on the minimum operating wavelength (λ≈8 μm) is overcome by utilising a novel injection barrier design to achieve lasing at λ=7.2 μm . In addition, we have deposited InAs monolayers in the active regions of a GaAs–AlAs quantum cascade laser to decrease the lasing transition wavelength. The InAs monolayers have a minimal effect on the upper laser level but decrease the confinement energy of the lower laser level. Thus a significantly reduced emission wavelength ( 8.3 μm compared with 11.2 μm ) is achieved whilst maintaining very similar laser performance.
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