Critical thickness of quantum well for observing Franz–Keldysh oscillation

Using scaling Fourier transformation (FT), we study the electro-reflectance spectra of quantum wells (QW) with well thickness from 200 to 1500 Å under a built-in electric field 50 kV/cm. For wider QWs, the FT of the spectra with energy scaled in (ℏω−Eg)3/2 exhibits Franz–Keldysh oscillation characteristic peaks. On the contrary, for the narrower QWs the characteristic peak of quantum confinement can be observed in FT with energy scaled in ℏω−Eg. By comparing the Fourier spectra, we set the transition width at 600 Å, which is much larger and more realistic than those reported previously.