Calculated stresses in multilayered heteroepitaxial structures

Abstract

A useful closed‐form expression for stresses within individual layers of a multilayer composite has been obtained as a function of position within the layer. Equal and isotropic elastic constants were assumed in the calculation, although the error introduced by this assumption is found to vary by no more than the difference in elastic constants. Unequal elastic constants may be handled via computer solutions. The stresses within heterojunction Al_xGa_1−xAs/GaAs lasers are calculated as an example of the technique. The addition of Al to the active GaAs region is shown to have a drastic effect upon the active‐region stress, changing it from tension to compression. This change of sign in stress is correlated with improvements in operating lifetimes of lasers.