Abstract
Understanding the physics of charge transport in organic materials and charge injection across organic-based interface is critically important for the development of novel organic electronics and optoelectronics. Despite extensive efforts devoted to the study of transport and injection phenomena in organic materials and interfaces, the physics of thermionic carrier injection across graphene/organic interface remains largely incomplete thus far. Here we construct a model of thermionic carrier injection across a graphene/organic Schottky interface based on the Lengevin theory of charge recombination and the detailed balance formalism. We show that, due to the strong electrostatic doping effect in graphene under the influence of an external gate voltage, the electrical current traversing the interface differs significantly from conventional bulk-metal/organic Schottky interface and the injection current can be efficiently modulated by a gate-voltage to achieve an on-off ratio well-exceed $10^7$. The model developed here shall provide a theoretical foundation for the understanding graphene/organic Schottky interface, thus paving the way towards the development of novel nanoscale graphene-hybrid organic electronic and optoelectronic devices.
Highlights
INTRODUCTIONThermionic charge injection across an interface formed between a metal and a crystalline semiconductor is governed by the celebrated Richardson-Schottky (RS) equation: JRS
Thermionic charge injection across an interface formed between a metal and a crystalline semiconductor is governed by the celebrated Richardson-Schottky (RS) equation: JRS = 4π m∗ h3 k2B T expB − e3V/4π εε0w, kBT (1)where J is the electrical current density, m∗ is the electron effective mass in the metal, and w is the depletion width in the semiconductor
At large applied bias voltage when the electrostatic doping effect in graphene becomes sufficiently strong, the field-induced enhancement of the thermionic injection current in graphene/organic Schottky interface becomes obvious as compared to the Scott and Malliaras (SM) model where such electrostatic doping effect negligible due to the strong screening of external electric field in conventional bulk metal
Summary
Thermionic charge injection across an interface formed between a metal and a crystalline semiconductor is governed by the celebrated Richardson-Schottky (RS) equation: JRS. In contrast to the RD model, the metal material parameters is completely absent in the pre-exponential factor in Equation (2) and the tunneling current is directly proportional to μ and N0, the mobility and the density of transport sites in the organic materials, respectively. Such unconventional μ-dependence, absent in the classic RS model, has been experimentally confirmed (Shen et al, 2001). We expand the SM model to the case of graphene/organic Schottky contact (see Figure 1A) where the Fermi level shifting due to gate and bias voltages is explicitly taken into account. The theoretical model developed here shall lay a useful theoretical foundation for the analysis, modeling, and design of graphene/organic electronic and optoelectronic devices
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