Quasi-Fermi level splitting in nanoscale junctions from ab initio

Abstract

The splitting of quasi-Fermi levels (QFLs) represents a key concept utilized to describe finite-bias operations of semiconductor devices, but its atomic-scale characterization remains a significant challenge. Herein, the non-equilibrium QFL or electrochemical potential profiles within single-molecule junctions obtained from the newly developed first-principles multispace constrained-search density functional formalism are presented. Benchmarking the standard non-equilibrium Green's function calculation results, it is first established that algorithmically the notion of separate electrode-originated nonlocal QFLs should be maintained within the channel region during self-consistent finite-bias electronic structure calculations. For the insulating hexandithiolate junction, the QFL profiles exhibit discontinuities at the left and right electrode interfaces and across the molecule the accompanying electrostatic potential drops linearly and Landauer residual-resistivity dipoles are uniformly distributed. For the conducting hexatrienedithiolate junction, on the other hand, the electrode QFLs penetrate into the channel region and produce split QFLs. With the highest occupied molecular orbital entering the bias window and becoming a good transport channel, the split QFLs are also accompanied by the nonlinear electrostatic potential drop and asymmetric Landauer residual-resistivity dipole formation. Our findings underscore the importance of the first-principles extraction of QFLs in nanoscale junctions and point to a new direction for the computational design of next-generation electronic, optoelectronic, and electrochemical devices.

Localized coherent phonon generation in monolayer MoSe2 from ultrafast exciton trapping at shallow traps

“…To analyze the nature of excitons trapped at V Se and V Se + O 2 , we next performed occupation-constrained DFT or DSCF calculations. [30][31][32][33][34] In Fig. 4(a), we present the potential energy surface diagram and spatial carrier distributions corresponding to the lattice displacements for V Se + O 2 obtained from the DSCF occupation constraint of promoting one electron from the highest occupied level to the lowest unoccupied level.…”

Quantum hybridization negative differential resistance from non-toxic halide perovskite nanowire heterojunctions and its strain control

“…Specifically, upon increasing the applied bias, we find that until = 0.5 V (NDR peak; Fig. 4 c middle panel) that corresponds to twice of the hole SBH (0.25 eV) the MIGS bound by quasi-Fermi levels (dotted lines) tilt symmetrically [ 22 ], maintaining the hybridization across the TMSGeI 3 channel and producing large transmission values. However, upon further increasing the bias to = 0.8 V (NDR valley; Fig.…”

“…Analyses on DFT-NEGF calculation output were performed using the Inelastica code and our in-house codes that implement the multi-space constrained-search DFT formalism [14,20,21,22].…”

“…Via shortening the distance between GeI3 electrodes, the hybridization of TMSGeI3-GeI3 interface states and accordingly their spatial extensions are substantially increased. This can be directly visualized through the molecular projected Hamiltonian eigenstates [20][21][22] that contribute most strongly to quantum transport (orange left triangle in Fig. 5b): Compared to the unstrained case, as shown in the top panel of Fig.…”

Raman Spectroscopy as a Simple yet Effective Analytical Tool for Determining Fermi Energy and Temperature Dependent Fermi Shift in Silicon

“…The term “Fermi-energy” is one of the most important concepts in modern science and is the backbone of semiconductor materials and device engineering. Accurate information about the position of Fermi level is essential for understanding semiconductor physics but determining its value experimentally is not straightforward and needs a lot of quantum mechanics. − Existing techniques to probe the Fermi-energy include ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy, valence band spectroscopy, electroreflectance spectroscopy, etc., in which one can determine its value at a given temperature . All these techniques have limitations and require lots of sample preparation and tedious calculations that restrict it to be used by nonexperts.…”