InGaAs/AlInAs strain-compensated Superlattices grown on metamorphic buffer layers for low-strain, 3.6 μm-emitting quantum-cascade-laser active regions

Short-wavelength (λ∼3.6 μm) quantum-cascade-laser (QCL) designs, employing a metamorphic buffer layer (MBL) on a GaAs substrate, have been developed for strong carrier confinement to the active regions, as a result of implementing the deep well and tapered active-region concepts. The strain · thickness product values for the quantum wells and barriers comprising the QCL active regions (ARs) are kept basically the same as those employed for longer wavelength (λ∼4.8 μm) QCL AR structures grown on InP substrates. Strain-compensated superlattice (SL) structures, representative of the QCL AR, are grown by metalorganic vapor phase epitaxy (MOVPE) on an AlInGaAs compositionally step-graded MBL. Structural characterization of the SL structures underscores the importance of reducing the top-surface roughness of the underlying MBL. Intersubband absorption has been observed for doped SL structures grown on hydride-VPE-grown MBLs.