FranzKeldysh
Franz-Keldysh effect refers to the change of the optical absorption edge of a semiconductor when a static electric field is applied. In a semiconductor with a band gap, the uniform electric field distorts electron and hole wavefunctions, enabling interband transitions that would be forbidden or weak in zero field. This leads to an extension of absorption below the nominal band edge through field-induced tunneling and to oscillatory modulations of the absorption above the edge, known as Franz–Keldysh oscillations.
The effect is described theoretically by solving the electron–hole problem in a linear potential; the solutions
Historically, the phenomenon was described by Franz in 1931 and independently by Keldysh in the 1950s; the
In practical terms, the Franz–Keldysh effect is a basis for electroabsorption modulators and other optoelectronic devices,