An alternative material system might be the key for higher operating temperatures of terahertz quantum cascade lasers (THz QCLs) [1]. At present, the material choice for THz QCLs is GaAs/AlGaAs, providing low conduction band offsets (~100-150 meV). This property is advantageous for terahertz active regions to keep the barrier thicknesses at reasonable values. In contrast, the material choice for midinfrared QCLs is InGaAs/InAlAs lattice-matched to InP for several reasons: the conduction band offset is 520 meV which allows short wavelength operation. A lower effective mass (0.043m0 for InGaAs, 0.067m0 for GaAs) results in larger dipole matrix elements and in turn yields higher optical gain. Despite the low effective InGaAs electron mass, THz QCLs demonstrated in this material system are not competitive since extremely thin barriers have to be employed in the active region [2] or a trade-off for a more robust design has to be done [3].

© 2011 Optical Society of America

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