Franz-Keldysh Effect

Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. The Franz-Keldysh effect is a change in optical absorption by a semiconductor when an electric field is applied. The effect is named after the German physicist Walter Franz and Russian physicist Leonid Keldysh. As originally conceived, the Franz-Keldysh effect is the result of wavefunctions leaking into the band gap. When an electric field is applied, the...
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Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. The Franz-Keldysh effect is a change in optical absorption by a semiconductor when an electric field is applied. The effect is named after the German physicist Walter Franz and Russian physicist Leonid Keldysh. As originally conceived, the Franz-Keldysh effect is the result of wavefunctions leaking into the band gap. When an electric field is applied, the electron and hole wavefunctions become Airy functions rather than plane waves. The Airy function includes a tail which extends into the classically-forbidden band gap. According to Fermi's Golden Rule, the more overlap there is between the wavefunctions of a free electron and a hole, the stronger the optical absorption will be. The Airy tails slightly overlap even if the electron and hole are at slightly different potentials. The absorption spectrum now includes a tail at energies below the band gap and some oscillations above it. This explanation does, however, omit the effects of excitons, which may dominate optical properties near the band gap.