Abstract
The weak-field effective-mass-approximation calculations of the absorption coefficient in the presence of an electric field for direct and indirect transitions at a normal () threshold are extended to an arbitrary orientation of the electric field in an anisotropic solid. To do this, a systematic method of evaluating density-of-states integrals arising in the electroabsorption or Franz-Keldysh effect is presented. Certain integrals obtained in prior calculations at the threshold which have not been previously evaluated are given in closed form. This method is also used to derive the change in absorption coefficient, , occuring at the saddle-point edges and , as well as the edge , for an arbitrary field direction in an anisotropic solid. It is shown that there is a direct correlation between for the and edges, and also for the and thresholds. Reduced masses of opposite signs, as in the and edges, give rise to two branches in .
- Received 21 February 1966
DOI:https://doi.org/10.1103/PhysRev.147.554
©1966 American Physical Society