The In0.53Ga0.47As∕AlAs0.56Sb0.44 heterostructure system is of significant interest for the development of high-performance intersubband devices due to its very large conduction band offset (ΔEc∼1.6eV) and lattice-matched compatibility with well-established InP-based waveguide technology. In this letter, we report the realization of In0.53Ga0.47As∕AlAs0.56Sb0.44 quantum cascade lasers emitting at λ∼4.3μm. The highest-performance devices have low-temperature (20K) threshold currents of ∼6kA∕cm2 and display laser action up to a maximum temperature of 240K, with a characteristic temperature of T0∼150K.
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We present high-power surface-emitting second-order distributed feedback quantum-cascade lasers in GaAs and InP material systems. The GaAs device, grown by molecular-beam epitaxy, showed single-mode peak output powers of 3 W at 78 K in pulsed operation. With the InP-based devices, which are grown by metalorganic vapor phase epitaxy, we obtained single-mode peak output powers of 1 W at room temperature. These are the highest output powers for surface emission of quantum-cascade lasers reported so far. The InP-based distributed feedback lasers also have very low threshold current densities and are working well above room temperature.
We have investigated the importance of intervalley (Γ–Χ) electron transfer between Γ-point quantum well states and X-point barrier states in GaAs-based quantum cascade lasers with indirect band gap AlAs barriers. A series of samples has been studied in which the energy separation between the coupled injector/upper laser levels and the lowest confined X state in the injection barrier is varied. 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) for the present laser design is overcome by utilizing a double injection barrier to achieve lasing at λ=7.2 μm.
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