Theory of normal-incidence absorption for the intersubband transition inn-type indirect-gap semiconductor quantum wells

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Abstract
We have studied systematically the normal-incidence-radiation absorption for the intersubband transition in the quantum well of n-type indirect-gap semiconductors. By a special choice of the coordinate system related to the sample growth direction, we have proposed a simple method to calculate the elements of the inverse effective-mass tensor. Using the concept of the invariance of the ellipsoidal constant-energy surface under coordinate transformations, the general expression for the absorption coefficient of the intersubband transition has been derived as a function of the sample growth direction. We have also investigated the maximal value of the normal-incidence radiation absorption, the optimal growth direction for quantum-well detectors, and the comparison between normal- and parallel-incidence-radiation absorptions. These are of great utility for designing and optimizing the quantum-well infrared detector for normally incident radiations.