Fluctuation-stimulated variable-range hopping

Abstract

Qualitatively new transport mechanism is suggested for hopping of carriers according to which the variable-range hopping (VRH) arises from the resonant tunneling between transport states brought into resonance by Coulomb potentials produced by surrounding sites with fluctuating occupations. A semiquantitative description of the hopping transport is given based on the assumption that fluctuations of energies of hopping sites have spectral density 1/f . Recently, it was suggested that fluctuations of site occupations in thermal equilibrium can cause essential energy fluctuations for sites participating in the hopping transport [1,2]. This idea was used to explain the lowfrequency noise with spectral density 1/f reported for hopping conductivity in p-Ge(Ga) and n-Ge(As) [1]. Due to the long-range character of the Coulomb potential, fluctuations in occupation numbers of some sites lead to essential fluctuations of energies of the surrounding sites. In Refs.[1,2], an attempt has been done to distinguish between the sites participating in the hopping transport (transport sites) and fluctuators, the latter being the sites which produce energy fluctuations on the transport sites, but do not directly participate in hopping processes. Comparison of experimental data with simple theoretical estimates [2] shows that the noise level is so large that each effective resistor on the transport cluster has relative fluctuations of the

Manifestation of Coulomb gap in two‐dimensional p‐GaAs–AlGaAs structures with filled lower or upper Hubbard bands

“…2. Using the model in [7] one obtains for the crossover temperature T c = (e 3 /κ 3/2 ) (g f /a) 1/2 ; thus in the vicinity of metal-insulator transition where a diverges, the crossover temperature decreases, which is in agreement with the experiment.…”

“…To the best of our knowledge the only attempt to develop an analytical model of correlated hopping within a semi-phenomenological approach was made in recent theoretical work by Kozub et al [7]. Following the ideas of [7] one comes to the E-S law and universal prefactor for 2D; however, the effective temperature in the E-S law appears to be different from the estimate given by Efros and Shklovskii and is given as T 0 ~ C 1 e 2 /κa. Thus instead of being purely nu- meric the coefficient C 1 appears to be:…”

Effect of screening on slow relaxation of excess conductance in two‐dimensional array of tunnel‐coupled quantum dots

“…becomes temperature independent and phononless hopping with universal conductivity prefactor G 0 = 2 / e h is observed [7]. However, as before, the Coulomb gap formation remains the main factor determining the temperature dependence of conductivity.…”

“…We got m ~ 0.3 (x=0.56) for the unscreened sample, which indicates that in the samples with the Coulomb gap the preexponential factor is virtually temperature-independent and conductivity is determined by the phononless hole hopping. Phononless mechanism of hopping conduction was proposed in [7] and involves stimulation of the electron transition between localized states by a charge fluctuation in close-located pairs -fluctuators. Interaction of fluctuator potential with carriers, participating in hopping, changes their energy and, hence, the probability of tunneling transition.…”

Correlated Variable Range Hopping in Doped GaAs, CdTe, Ge and Si

“…D ES /D multi X ffi 10. A completely different approach of Coulomb correlation was recently proposed by the ''fluctuation stimulated variable-range hopping" [7] and in [8], which also results in a significantly reduced width of the Coulomb gap. From Eqs.…”