Oscillatory behavior of the continuum states in ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/GaAs quantum wells due to capping-barrier layers of finite size

Photoreflectance spectra of ${\mathrm{In}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/GaAs single quantum wells have shown above-barrier oscillations, of amplitude comparable to those of transitions involving only bound states. The spacing between the oscillation extrema increases with energy according to the relation ${\mathit{E}}_{\mathit{n}}$=${\mathit{E}}_0$+α ${\mathit{n}}^2$ for the nth extremum. These results demonstrate experimentally that the continuum states are influenced by the finite extent of the barrier on the side of the well which terminates the device (the cap layer). The high potential at the surface of the cap and the finite size of the cap layer produce quantum interference in the continuum state wave functions which leads to oscillations in the probabilities of finding the carriers in the various regions of the structure. The modulation is expected to be determined mainly by ${\sin }^2$(${\mathit{k}}_{\mathit{b}}$t), where t is the thickness of the cap layer and ${\mathit{k}}_{\mathit{b}}$ is the wave vector in the barrier, and includes the carrier effective mass. Depending on the value of t, these cap-related oscillations are observed for the various types of carriers in photoreflectance experiments; their visibility depends on the well width.