Dielectric response induced by intersubband transitions in quantum wells: Transmission ellipsometry studies at Brewster angle

Abstract

The potential of infrared transmission spectroscopic ellipsometry is demonstrated for the case of intersubband transitions between the first and second upper-lying conduction-band states in a quantum well. Using the substrate-ambient interface as a Brewster polarizer, multiple reflections in the sample are modeled to occur only at a bare substrate-ambient interface. The ellipsometrically measured polarization ratio is related to the transfer-matrix elements of the overlayer by treating the latter as an effective medium uniaxial layer, grown on top of an isotropic substrate. The above approach is applied for a 60 period n-GaAs/Al0.3Ga0.7As (88 Å/130 Å) quantum-well stack, grown on a semi-insulating GaAs substrate. The experimentally extracted dielectric response of the overlayer to the propagating extraordinary beam is compared to the spectrum, calculated using a Lorentzian oscillator, centered at 1045 cm−1 with broadening of 100 cm−1, as expected from the engineered potential.