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

Abstract

The direct way to investigate the effect of an electric field F on the optical properties of a quantum well (QW) is to change the well width(Miller et al 1986 Phys. Rev. B 33 6976). Photoreflectance studies of a 100 angstrom and a 250 angstrom Ge/GeSi modulation doped QWs possessing $10_{4}V cm^{-1}$ perpendicular fields are presented. This technique modulates the QW electro-absorption, which we compute using wave functions obtained from a 8 x 8 k . p calculation. They are shown to have a pronounced tunnelling into the band gap in the 250 angstrom QW, in contrast to the 100 angstrom QW. Kramers-Kronig analysis is used to determine the corresponding changes in the QW refractive index, and overall reflection from the entire sample (including barriers) is obtained within a 2 x 2 matrix formalism. In a QW of width $L_{z}$, the Franz-Keldysh effect is expected to be important in an energy interval extending from near the bandgap $E_{o} to E_{o} + eFL_{z}$. Its role in altering QW optical properties as a function of $L_{z}$, is tested by comparing calculated and experimental spectra in this interval

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