Strong far-infrared intersubband absorption under normal incidence in heavily n-type doped nonalloy GaSb-AlSb superlattices

Abstract

We report on long‐wavelength intersubband absorption under normal incidence in heavily doped binary‐binary GaSb‐AlSb superlattices. Due to a small energy difference between the ellipsoidal L valleys in GaSb and the low‐density‐of‐states Γ minimum, electrons spill over from the first Γ subband into the higher‐energy L subband in GaSb wells, where they are allowed to make an intersubband transition under normally incident radiation. A peak fractional absorption per quantum well of 6.8×10⁻³ (absorption coefficient α≊8500 cm⁻¹) is observed at λ≊15 μm for a sheet concentration of 1.6×10¹² cm⁻²/well.