Intersubband absorption from InGaAlAs/InAlAs multiple quantum-well structures grown by molecular-beam epitaxy

The intersubband absorption from the InGaAlAs/InAlAs multiple quantum-well structures, lattice matched to InP, for the long-wavelength infrared detection has been investigated. It is found that the strong absorption resulting from the bound-to-bound transition in the quaternary material is observable and the wavelength of the absorption varies with the well width while the barrier width remains unchanged. The photoluminescence results indicate that the absorption originates from the transition of the electrons from the ground energy level to the first excited energy level in the conduction band of the well material. Our experimental results are also in good agreement with the theoretical estimation based on the simple finite barrier model.