Abstract
The interface between a metal and a semiconductor is known as Schottky contact and a key factor in semiconductor technologies. Those interfaces normally build an energetic barrier, which is responsible for the exponential current voltage dependence. Analytical models often describe the right trend for the description of the Schottky barrier height, but fail to predict the barrier properties quantitatively correct. To overcome this problem atomistic and quantum mechanical approaches are required such as the here applied density functional theory combined with the non-equilibrium Greens function method. So far, these methods have rarely been applied to wide band gap metal oxides, which leads to a lack in the understanding of oxide electronics. The presented study deals with the image force induced Schottky barrier lowering of a SrTiO3/Pt interface as a model system for wide band gap metal-oxide Schottky contacts. The Schottky barrier lowering is investigated for the case of different doping concentrations/positions and for different voltages. From a defect chemical point of view, oxygen vacancies act as donors in many metal oxides and dominate the electronic conduction in oxide electronics. Consequently, we investigated the Schottky barrier lowering induced by oxygen vacancies. The second doping mechanism is achieved in the sense of classical doping using Nb impurities, which form a conventional n-type donor. The atomistic simulation reveals the Schottky barrier lowering effect for both type of dopants. The results are compared to a standard analytical model regarding the Schottky barrier lowering.
Highlights
Metal semiconductor interfaces are crucial within many applications of electronic devices
By tracing the edge between the colored and the black region, the band bending can be roughly determined. It shows that a conduction band bending occurs from the SrTiO3/Pt interface to the position of the oxygen vacancy, giving rise to the existence of a depletion zone, which is expected from classical semiconductor theory
The atomistic simulation results show the same properties as expected from classical semiconductor theory. We see this result as a validation for both, the established theory of Schottky contact formation and that our density functional theory (DFT) simulation model is able to represent the electronic properties of the SrTiO3/Pt contact
Summary
Metal semiconductor interfaces are crucial within many applications of electronic devices. ∆φ(V, N) = e e3N (Vin − V) 8π2ε30ε3r for the Schottky barrier lowering.[32] In equation (1), N is the doping concentration, V is the electrostatic potential ε0εr is the permittivity of the semiconductor, e is the elementary charge, Vin is the builtin potential defined by the difference of the bulk conduction band level and the Schottky barrier height.[32] Especially Schottky contacts based on a high work function material and a wide band gap intrinsically form a high built-in potential/high electric field. We investigate the Schottky barrier lowering of a SrTiO3/Pt system with different types of dopants under an applied electric field using atomistic simulations based on DFT combined with the non-equilibriums Green’s function (NEGF) formalism.
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