No abstract

Copper nanowires are widely used as on-chip interconnects due to superior conductivity. However, with aggressive Cu interconnect scaling, the diffusive surface scattering of electrons drastically increases the electrical resistivity. In this work, we studied the electrical performance of Cu thin films on different materials. By comparing the thickness dependence of Cu films resistivity on MoS2 and SiO2, we demonstrated that two-dimensional MoS2 can be used to enhance the electrical performance of ultrathin Cu films due to a partial specular surface scattering. By fitting the experimental data with the theoretical Fuchs-Sondheimer (FS) model, we claimed that the specularity parameter at the Cu/MoS2 interface is p ≈ 0.4 in the temperature range 1.8K < T < 300K. Furthermore, first principle calculations based on the density functional theory (DFT) indicates that there are more localized states at the Cu/amorphous SiO2 interface than the Cu/MoS2 interface which is responsible for the higher resistivity in the Cu/SiO2 heterostructure due to more severe electron scattering. Our results suggest that Cu/MoS2 hybrid is a promising candidate structure for the future generations of CMOS interconnects.

Orientation effects on the specific resistance of copper grain boundaries are studied systematically with two different atomistic tight binding methods. A methodology is developed to model the specific resistance of grain boundaries in the ballistic limit using the Embedded Atom Model, tight binding methods and non-equilibrum Green's functions (NEGF). The methodology is validated against first principles calculations for thin films with a single coincident grain boundary, with 6.4% deviation in the specific resistance. A statistical ensemble of 600 large, random structures with grains is studied. For structures with three grains, it is found that the distribution of specific resistances is close to normal. Finally, a compact model for grain boundary specific resistance is constructed based on a neural network. * valencid@purdue.edu 1 arXiv:1701.04897v3 [cond-mat.mtrl-sci]

The performance of nitride‐based light emitting diodes is determined by carrier transport through multi‐quantum‐well structures. These structures divide the device into spatial regions of high carrier density, such as n‐GaN/p‐GaN contacts and InGaN quantum wells, separated by barriers with low carrier density. Wells and barriers are coupled to each other via tunneling and thermionic emission. Understanding of the quantum mechanics‐dominated carrier flow is critical to the design and optimization of light‐emitting diodes (LEDs). In this work a multi‐scale quantum transport model, which treats high densities regions as local charge reservoirs, where each reservoir serves as carrier injector/receptor to the next/previous reservoir is presented. Each region is coupled to its neighbors through coherent quantum transport. The non‐equilibrium Green's function (NEGF) formalism is used to compute the dynamics (states) and the kinetics (filling of states) of the entire device. Electrons are represented in multi‐band tight‐binding Hamiltonians. The I–V characteristics produced from this model agree quantitatively with experimental data. Carrier temperatures are found to be about 60 K above room temperature and the quantum well closest to the p‐side emits the most light, in agreement with experiments. Auger recombination is identified to be a much more significant contributor to the LED efficiency droop than carrier leakage.

State-of-the-art industrial semiconductor device modeling is based on highly efficient Drift-Diffusion (DD) models that include some quantum corrections for nanodevices. In contrast, latest academic quantum transport models are based on the non-equilibrium Green’s function (NEGF) method that covers all coherent and incoherent quantum effects consistently. Carrier recombination and generation in optoelectronic nanodevices represent an immense numerical challenge when solved within NEGF. In this work, the numerically efficient Büttiker-probe model is expanded to include electron–hole recombination and generation in the NEGF framework. Benchmarks of the new multiple-particle Büttiker probe method against state-of-the-art quantum-corrected DD models show quantitative agreements except in cases of pronounced tunneling and interference effects.