Screening within accumulation layers of molecular semiconductors

Abstract

In organic field-effect transistors, conductivity is achieved by electronically injected charges that form high-density accumulation layers. We report self-consistent calculations of Poisson's equation, carrier statistics, and the Drude permittivity of the carrier gas at the interface between semiconductors and insulators. The results show that the injected carriers efficiently screen local potentials. Additionally, the AC permittivity of the carriers reduces electrical fields particularly at frequencies of several THz. This dynamic screening may affect the formation of large polarons and the transient localization of carriers.

Terahertz Electromodulation Spectroscopy for Characterizing Electronic Transport in Organic Semiconductor Thin Films

“…Compared to silicon, where electron mobilities can reach μ ≈ 1500 cm 2 /Vs, the mobilities in organic semiconductors rarely exceed 10 cm 2 /Vs. Furthermore, organic field-effect structures have accumulation layers that are only a few nanometers thick [18,37]. Both lead to diminutive sheet conductivities σ 2D = eμ n 2D and thus to a weak interaction between the THz radiation and the carriers within the organic semiconductor.…”

Impact of surface roughness on conduction in molecular semiconductors

“…The overall potential landscape within the device is obtained by the self-consistent solution of the Poisson equation by considering the carrier statistics that regulate the local charge density. 15 Usually, Maxwell-Boltzmann statistics are applied. In this work, however, the Fermi energies approach the valence band and Fermi-Dirac statistics are appropriate.…”

“…The computational costs are efficiently reduced by applying listing concepts. 15,18 All data presented are obtained using a damped Newton-Raphson algorithm combined with the method of successive overrelaxation.…”