Intersubband optical absorption in strained double barrier quantum well infrared photodetectors

A systematic theoretical investigation of intersubband optical absorption i n AlGaAs/AlAs/InGaAs strained double barrier quantum well is presented for the first time, Electron states are calculated within the effective mass ap proximation which includes the effects of subband nonparabolicity and strai n, and found to be in good agreement with experiments. Intersubband optical absorption is investigated using the density matrix formalism with the int rasubband relaxation taken into account. Analytical formulas are given for electron energies, absorption coefficient, and responsivity, Subband nonpar abolicity and elastic strain are found to significantly influence both elec tron states and intersubband optical absorption. The peak absorption wavele ngth 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 Angstrom. Th e results are useful for design and improvement of the performance of quant um well infrared photodetectors operating in the important wavelength regio n between 1.5 and 4 mu m.