Intersubband transitions in single AlGaAs/GaAs quantum wells studied by Fourier transform infrared spectroscopy

Infrared intersubband absorption in modulation-doped MOVPE-grown AlxGa1−xAs/GaAs single-quantum wells have been studied by Fourier transform infrared spectroscopy. High signal to noise ratio was obtained by utilizing the multiple internal reflection (MIR) technique and a quantitative model of the absorption for this geometry was developed. Overlapping from multiphonon absorption was eliminated by using radiation polarized in two orthogonal directions and taking the difference between the resulting spectra, only one of them exhibiting the intersubband peak. The absorption wavelengths and intensities were fitted to theoretical expressions and the dimensions of the quantum wells were compared with independent determinations by photoluminescence, double crystal x-ray diffraction, and Hall-effect measurements. A narrow linewidth of about 6 meV was measured, corresponding to a 0.1-ps lifetime of electrons in the excited state.