Abstract
In this experiment 180-Å GaAs/AlAs quantum wells were grown with an Si concentration of 1012/cm2 δ-doped at the edge of the wells. The δ-doping created an internal electric field across the wells, breaking the reflection symmetry about the center of the well and permitting the occurrence of normally disallowed intersubband transitions between like-parity envelope states of electrons within the wells.1 The 180-Å quantum well size was chosen so that the energy of the transition between the first and third conduction subband was resonant with the light from a CO2 laser. By applying an external electric field normal to the plane of the quantum wells, modulation of the absorption of 9.7-μm light passing through the sample was observed, as the applied field augmented or counteracted the internal field. The measurements were taken at various temperatures and duty cycles to identify extraneous effects such as thermal modulation of the free-carrier absorption. The modulation was temperature and duty-cycle independent for low temperatures and duty cycles, and it showed the proper polarization dependence and magnitude as predicted by theory. This was also corroborated by spectrometer measurements of the absorption coefficient in zero external field.
© 1991 Optical Society of America
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