Simple theoretical analysis of the interband optical absorption coefficient in wide-gap semiconductors in the presence of an external electric field and its dependence on a longitudinal magnetic field

An attempt is made to present a simplified theoretical analysis of the interband optical absorption coefficient (OAC) due to a constant uniform electric field on the basis of the electron wave vector dependence of the optical matrix element (OME) for the incident photon energy, (h omega), below and above the band-gap (E,). It has been found, taking n-GaAs as an example for numerical computation, that the expression of the OAC exhibits an exponential fall-off with the electric field and the photon energy without the consideration of the Wannier-Stark levels, which generally exists in a band due to the external electric field. The effect of a longitudinal magnetic field on the OAC is also studied on the basis of the fact that the transverse wave vector (k(perpendicular to)) is quantized due to parallel magnetic field and is conserved in the interband optical transition of electrons. Similar results, such as singularity for the case h omega < E-g in the OAC and the oscillations in the OAC for the case h omega > E-g in presence of electric field are also obtained with modifications in the expressions for the OAC in presence of electric and parallel magnetic fields. Present study explains the modification of the band-gap of the semiconductor in the presence of electric and parallel magnetic fields, respectively. The numerical analyses are performed and discussed in details taking n-GaAs as an example. (c) 2006 Elsevier B.V. All rights reserved.