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 104 V/cm perpendicular electric fields. Qualitatively very different spectra are obtained from samples of well-width 100 and 250 . Comparing the wavefunctions calculated from an 8 × 8 k.p theory, we find that while they remain confined in the narrower 100 QW, the electric field causes them to tunnel into the forbidden gap in the 250 \ 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.
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