Percolation description of charge transport in amorphous oxide semiconductors

Abstract

The charge transport mechanism in amorphous oxide semiconductors (AOS) is a matter of controversial debates. Most theoretical studies so far neglected the percolation nature of the phenomenon. In this article, a recipe for theoretical description of charge transport in AOSs is formulated using the percolation arguments. Comparison with the previous theoretical studies shows a superiority of the percolation approach. The results of the percolation theory are compared to experimental data obtained in various InGaZnO materials revealing parameters of the disorder potential in such AOS.

Analytical Surface Potential-Based Compact Model for Independent Dual Gate a-IGZO TFT

“…where g(E) is the density of states (DOS) energy distribution, E = 0 corresponds to the mobility edge, the first term on the right-hand side of (2) describes the density of extended states with the positive E [11], and the second term describes the density of localized states with the negative E, which is related to the disorder and the Urbach tail [12], N t is the total concentration of localized states, the value g c = 1.4×10 21 cm −3 eV −3/2 has been reported for a-IGZO thin films [13], k B is Boltzmann's constant, T 0 is the characteristic temperature of the exponential DOS, and E F (z) is the quasi-Fermi level.…”

Influence of Thermal Post-deposition on Trap States in Sol-gel Indium Zinc Oxide TFTs

“…It may depend on temperature and electron concentration. For the sake of simplicity, we consider µ 0 a constant and it serves as a fitting parameter for our model [25], [26].…”

“…Charge transport in inorganic TFTs is primarily modeled using percolation theory or trap-limited band transport, also called multiple trap and release (MTR). Percolation theory in oxides is best described assuming the random band edge model [25], [26]. In this model, the IGZO conduction band edge (E m ) is assumed to have potential barriers and wells due to Ga 3+ and Zn 2+ ions, which is represented by a Gaussian distribution, where δ represents the standard deviation of the distribution.…”

“…In the case of very high disorder or at low temperatures (kT << eδ), the conductivity is dominated by the mobile electrons which have more energy than the percolation threshold energy level (E p ). The conductivity is then the average of the regional conductivities where E m > E p [26], [27]. Under low disorder and at high temperatures (kT ∼ eδ), the conduction electrons have high thermal energy and their energy is comparable to the barrier distribution width.…”

“…Under these conditions, the barrier distribution plays no role [27]. In cases where the temperature is high or the disorder is low, MTR can be readily used to describe the charge transport [26], [28]- [30]. Here, the charge transport is primarily through the extended states above the conduction band edge (also called the mobility edge or transport level).…”