Effect of well-width on the electro-optical properties of a quantum well

Abstract

We record photoreflectance from Ge/GeSi modulation doped quantum wells possessing $10^4$ V/cm perpendicular electric fields. Qualitatively very different spectra are obtained from samples of well-width 100 Åand 250 Å. Comparing the wavefunctions calculated from an $8\times 8$ \textbf{k.p} theory, we find that while they remain confined in the narrower 100 ÅQW, the electric field causes them to tunnel into the forbidden gap in the 250 Å well. This implies that the samples should show a transition from the quantum confined Franz-Keldysh effect to the bulk-like Franz-Keldysh effect. Close to the band-edge where Franz-Keldysh effects are important, simulated photoreflectance spectra reproduce the essential features of the experiment, without any adjustable parameters.

8 pages, 8 figures. Submitted to Phys. Rev. B