Photoconductivity ofInxAl1−xAsparabolic quantum wells in the optical-phonon regime

We present far-infrared photoconductivity (PC) measurements for a two-dimensional electron gas (2DEG) in an ${\mathrm{In}}_{x}{\mathrm{Al}}_{1\ensuremath{-}x}\mathrm{As}$ parabolic quantum well grown on a GaAs substrate. By applying a magnetic field, we observe a response in the longitudinal resistance of the 2DEG caused by the bolometric effect of the cyclotron resonance (CR). We can tune the CR across the optical phonon regimes of both ${\mathrm{In}}_{x}{\mathrm{Al}}_{1\ensuremath{-}x}\mathrm{As}$ and GaAs. In this regime, we observe both optical effects from the multilayered structure and effects of the coupling between the 2DEG and the longitudinal optical phonons. We compare our results to dielectric calculations and find that the PC signal arises from the absorption in the 2DEG but not from the total absorption of the multilayers.