Intersubband transitions in GaAs-AlxGa1−xAs modulation-doped superlattices

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Abstract
We have investigated infrared absorptions between electron subbands in GaAs‐AlxGa1−xAs modulation‐doped superlattices with constant layer thicknesses (70 Å for the GaAs layer and 180 Å for the AlxGa1−xAs layer) and a wide Al concentration range from 0.3 to 0.7. Sharp resonance absorptions from the ground state to the first excited state were detected in all samples. The transition energy increases from 130 to 170 meV as the Al concentration increases. From the observed transition energies (subband spacing) we estimate that the conduction‐band discontinuity is around 63% of the difference between the direct band‐gap energy of GaAs and that of AlxGa1−xAs in the Al concentration range used here.