Intersubband absorption in n-doped InAs/AlSb multiple-quantum-well structures

Well-thickness dependence of intersubband absorption energies is investigated in $n$-doped InAs/AlSb multiple-quantum-well structures grown by molecular-beam epitaxy. Decreasing the InAs well thickness from 18 to 9 monolayers, the absorption peak shifts from 3.31 μm (375 meV) to 1.98 μm (627 meV). These absorption energies are found to be larger than those of the corresponding spatially indirect band gap between the electron ground state in the InAs well and the heavy-hole ground state in the AlSb barrier. Intersubband transition energies are calculated self-consistently using multiband $k⋅p$ calculation combined with Poisson equation, and compared with the experimental results.