Short-wavelength intersubband absorption in strain compensated InGaAs/AlAs quantum well structures grown on InP

We have studied intersubband absorption in strain compensated ${\mathrm{In}}_x{\mathrm{Ga}}_{\text{1−x}}{\mathrm{As/AlAs/In}}_y{\mathrm{Al}}_{\text{1−y}}\mathrm{As}$ multiple quantum wells and superlattices grown on InP. X-ray diffraction shows that the layers are pseudomorphically strained and exhibit slight compositional grading of the interfaces. Owing to the high AlAs barriers, the intersubband absorption can be tailored to wavelengths shorter than 2 μm. In some samples, a small, but non-negligible absorption is also observed with $s$ -polarized light.