Nonequilibrium coherent potential approximation for electron transport

Accounting for the effects of disorder on the transport properties of electronic devices is indispensable for comparison with experiment. However, theoretical treatment of disorder presents essential difficulty because the disorder breaks the periodicity of the system. The coherent potential approximation (CPA) solves this problem by replacing the disordered medium with a periodic effective medium. However, calculating the electron current within CPA requires summing scattering diagrams to infinite order called vertex corrections. In this work we reformulate CPA for nonequilibrium electron transport. This approach, based on the nonequilibrium Green's function formalism, greatly simplifies the treatment of disordered transport by eliminating the vertex corrections.

Figure 1

Schematic view of the two-probe setup consisting of two electrodes and a scattering region. In this case, the scattering region is a tunnel barrier with a disordered layer in the middle.

Figure 2

Density of states in the barrier for weak (a) and strong (b) scattering. Both low and high impurity concentration are shown.

Figure 3

Current density as a function of applied bias (a) and transmission as a function of energy (b) for strong scattering and high impurity concentration. The result for CPA, CPA with VCs to finite order, CPA with VCs to infinite order, and NE-CPA are plotted. The line of the CPA with full VCs coincides with the NE-CPA line.