DIELECTRIC RESPONSE INDUCED BY INTERSUBBAND TRANSITIONS IN QUANTUM-WELLS - TRANSMISSION ELLIPSOMETRY STUDIES AT BREWSTER-ANGLE

The potential of infrared transmission spectroscopic ellipsometry is d emonstrated for the case of intersubband transitions between the first and second upper-lying conduction-band states in a quantum well. Usin g the substrate-ambient interface as a Brewster polarizer, multiple re flections in the sample are modeled to occur only at a bare substrate- ambient interface. The ellipsometrically measured polarization ratio i s 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-G aAs/Al0.3Ga0.7As (88 angstrom/130 angstrom) quantum-well stack, grown on a semi-insulating GaAs substrate. The experimentally extracted diel ectric response of the overlayer to the propagating extraordinary beam is compared to the spectrum, calculated using a Lorentzian oscillator , centered at 1045 cm- with broadening of 100 cm-1, as expected from t he engineered potential.