Nonlinear acoustic and microwave absorption in disordered semiconductors

Abstract

Nonlinear hopping absorption of ultrasound and electromagnetic waves in amorphous and doped semiconductors is considered. It is shown that even at low amplitudes of the electric (or acoustic) field the nonlinear corrections to the relaxational absorption appear anomalously large. The physical reason for such behavior is that the nonlinear contribution is dominated by a small group of close impurity pairs having one electron per pair. Since the group is small, it is strongly influenced by the field. An external magnetic field strongly influences the absorption by changing the overlap between the pair components' wave functions. It is important that the influence is substantially different for the linear and nonlinear contributions. This property provides an additional tool to extract nonlinear effects.

Fluctuator Model of Memory Dip in Hopping Insulators

“…One should note that the actual screening of the Coulomb interaction is associated with the polarization of electronic states rather than real hopping processes formally making static dielectric constant equal to infinity [37]. This is so called resonant contribution [38] similar to the one in dielectric glasses [39].…”

“…In the absence of fluctuators the density function of sufficiently large dipoles, a < r < d with the energy, E ∼ k B T , can be approximated by [14,38] …”

“…Let those dipoles be characterized by the density function F (∆, r) depending on their energy, ∆ and size r. This size determines the tunneling amplitude of electron between two localized states, ∆ 0 ≈ E 0 e −r/a . Then one can approximate the contribution of interest to the dielectric constant as (c. f. [26,27])…”

“…( 6) are identical to resonant and relaxational contributions to the dielectric constant in amorphous solids [2,10] and the latter contribution is more significant because it is determined by lowest energies of pairs. In the absence of fluctuators the density function of sufficiently large dipoles, a < r < d is given by [26,27]…”