Observation of Normal-Incidence Intersubband Absorption in N-Type Al0.09Ga0.91Sb Quantum Wells

Normal-incidence intersubband absorption has been observed in n-type Al0.09Ga0.91Sb quantum wells, as predicted by our previous calculation. The quantum wells were grown on (100)-GaSb and (100)-GaAs substrates and contain an electron sheet density of approximately 7×1011 cm-2. The electrons occupy a two-dimensional L-point subband having ellipsoidal Fermi surfaces. For 7.0-nm-wide quantum wells, the absorption peak occurs at 870 cm-1 (11.5 m), the peak fractional absorption per quantum well is 0.06%, and the full width at half maximum of the absorption profile is 30 meV. The measured absorption strength is within 12% of the theoretical calculation, which was based on the effective-mass method.