Intersubband optical absorption in strained double barrier quantum well infrared photodetectors

A systematic theoretical investigation of intersubband optical absorption in AlGaAs/AlAs/InGaAs strained double barrier quantum well is presented for the first time. Electron states are calculated within the effective mass approximation which includes the effects of subband nonparabolicity and strain, and found to be in good agreement with experiments. Intersubband optical absorption is investigated using the density matrix formalism with the intrasubband relaxation taken into account. Analytical formulas are given for electron energies, absorption coefficient, and responsivity. Subband nonparabolicity and elastic strain are found to significantly influence both electron states and intersubband optical absorption. The peak absorption wavelength is found to decrease linearly if the In composition is increased, and an approximate formula is given. Electron states and optical absorption are affected by the inner barrier thickness if it is less than 40 A. The results are useful for design and improvement of the performance of quantum well infrared photodetectors operating in the important wavelength region between 1.5 and 4 /tin.