Grazing-angle intersubband absorption in n-doped GaAs multiple quantum wells

We present a study of the mid-infrared intersubband absorption in n-doped G aAs/AlxGa1-xAs multiple quantum wells (MQWs) for various internal incident angles. Above 45 degrees incidence we show that the traveling-wave approxim ation is not valid: redshifts of the absorption peak are observed, striking ly additional peaks appear for thick structures, and the strength of absorp tion does not necessarily increase with the incident angle. The understandi ng of such complex absorption behavior requires considering the quantum wel l as an absorbing uniaxial material and taking into account the multiple re flections of the light inside the MQW.