Phonon-assisted two-photon absorption in the presence of a dc-field: the
nonlinear Franz–Keldysh effect in indirect gap semiconductors

Author

Hernando Garcia1 and Ramki Kalyanaraman2

Affiliations

1 Department of Physics, Southern Illinois University, Edwardsville, IL 62026,
USA

2 Department of Physics, Washington University in St Louis, St Louis, MO 63130,
USA

Hernando Garcia and Ramki Kalyanaraman 2006 J. Phys. B: At. Mol. Opt. Phys. 39
2737

The two-photon absorption coefficient of an indirect gap semiconductor
(phonon-assisted two-photon absorption) in the presence of a strong dc-electric
field applied perpendicular to the direction of propagation of the optical field
is calculated using the formalism developed elsewhere (Aspnes 1996 Phys. Rev. B.
147 554). We show that depending on the type of transition (i.e.,
allowed–allowed, allowed–forbidden or forbidden–forbidden), the absorption
coefficient followed different dispersion relations. In the limit of a weak
electric field, we recovered results previously calculated using perturbation
theory. In the strong dc-field regime, we found that below the rescaled energy
gap given by Eg/N, where N is the number of photons, the tunnelling effect is
present, but to our surprise, above the rescaled gap, the Franz–Keldysh
oscillations are present only for the allowed–allowed transition. This absence
of the oscillations in the allowed–forbidden and forbidden–forbidden transitions
is possible due to the weak coupling of the tails of the electron and hole
wavefunctions.

Compound figure of merit for photonic applications of metal nanocomposites

Hernando Garciaa

Department of Physics, Southern Illinois University, Edwardsville, Illinois
62026

Hare Krishna and Ramki Kalyanaraman

Department of Physics, Washington University in St. Louis, St. Louis, Missouri
63130

Selecting nanocomposites for photonic switching applications requires optimizing
their thermal,

nonlinear, and two-photon absorption characteristics. The authors simplify this
step by defining a

compound figure of merit FOMC for nanocomposites of noble metals in dielectric
based on criteria

that limit these structures in photonic applications, i.e., thermal heating and
two-photon absorption.

The device independent results predict extremely large values of FOMC for a
specific combination

of the metal and insulator dielectric constants given by h= 1− 2 /2, where h is
the dielectric

constant of the host and 1 and 2 are the real and imaginary parts for the metal.