Inter-sub-band absorption in GaAs/AlGaAs single quantum wells

The observation of resonant inter-sub-band absorption in Al x Ga 1-x As/GaAs single quantum wells using a total internal reflection geometry is reported. It is shown that strong absorption is obtained provided that a large optical electrical field perpendicular to the quantum wells is generated. Such conditions occur when the well is close to the reflecting boundary and reflection occurs at a semiconductor/metal interface, but not when reflection occurs at a semiconductor/vacuum interface. The optical properties of the whole structure can be quantitatively described by considering the system as a multi-layer dielectric stack.