Theoretical investigation of direct and phonon-assisted tunneling currents in InAlGaAs-InGaAs bulk and quantum well interband tunnel junctions for multi-junction solar cells

Direct and phonon-assisted tunneling currents in InAlGaAs-InGaAs bulk and double quantum well interband tunnel heterojunctions are simulated rigorously using the non-equilibrium Green's function formalism for coherent and dissipative quantum transport in combination with a simple two-band tight-binding model for the electronic structure. A realistic band profile and associated built-in electrostatic field is obtained via self-consistent coupling of the transport formalism to Poisson's equation. The model reproduces experimentally observed features in the current-voltage characteristics of the device, such as the structure appearing in the negative differential resistance regime due to quantization of emitter states. Local maps of density of states and current spectrum reveal the impact of quasi-bound states, electric fields and electron-phonon scattering on the interband tunneling current. In this way, resonances appearing in the current through the double quantum well structure in the negative differential resistance regime can be related to the alignment of subbands in the coupled quantum wells.Comment: 4 pages, 5 figure

Engineering interband tunneling in nanowires with diamond cubic or zincblende crystalline structure based on atomistic modeling

We present an investigation in the device parameter space of band-to-band tunneling in nanowires with a diamond cubic or zincblende crystalline structure. Results are obtained from quantum transport simulations based on Non-Equilibrium Green's functions with a tight-binding atomistic Hamiltonian. Interband tunneling is extremely sensitive to the longitudinal electric field, to the nanowire cross section, through the gap, and to the material. We have derived an approximate analytical expression for the transmission probability based on WKB theory and on a proper choice of the effective interband tunneling mass, which shows good agreement with results from atomistic quantum simulation.Comment: 4 pages, 3 figures. Final version, published in IEEE Trans. Nanotechnol. It differs from the previous arXiv version for the title and for some changes in the text and in the reference

Theory and simulation of quantum photovoltaic devices based on the non-equilibrium Green's function formalism

This article reviews the application of the non-equilibrium Green's function formalism to the simulation of novel photovoltaic devices utilizing quantum confinement effects in low dimensional absorber structures. It covers well-known aspects of the fundamental NEGF theory for a system of interacting electrons, photons and phonons with relevance for the simulation of optoelectronic devices and introduces at the same time new approaches to the theoretical description of the elementary processes of photovoltaic device operation, such as photogeneration via coherent excitonic absorption, phonon-mediated indirect optical transitions or non-radiative recombination via defect states. While the description of the theoretical framework is kept as general as possible, two specific prototypical quantum photovoltaic devices, a single quantum well photodiode and a silicon-oxide based superlattice absorber, are used to illustrated the kind of unique insight that numerical simulations based on the theory are able to provide.Comment: 20 pages, 10 figures; invited review pape

Simulation of nanostructure-based and ultra-thin film solar cell devices beyond the classical picture

In this paper, an optoelectronic device simulation framework valid for arbitrary spatial variation of electronic potentials and optical modes, and for transport regimes ranging from ballistic to diffusive, is used to study non-local photon absorption, photocurrent generation and carrier extraction in ultra-thin film and nanostructure-based solar cell devices at the radiative limit. Among the effects that are revealed by the microscopic approach and which are inaccessible to macroscopic models is the impact of structure, doping or bias induced nanoscale potential variations on the local photogeneration rate and the photocarrier transport regime.Comment: 15 pages, 10 figure

Strong-field Phenomena in Periodic Systems

The advent of visible-infrared laser pulses carrying a substantial fraction of their energy in a single field oscillation cycle has opened a new era in the experimental investigation of ultrafast processes in semiconductors and dielectrics (bulk as well as nanostructured), motivated by the quest for the ultimate frontiers of electron-based signal metrology and processing. Exploring ways to approach those frontiers requires insight into the physics underlying the interaction of strong high-frequency (optical) fields with electrons moving in periodic potentials. This Colloquium aims at providing this insight. Introduction to the foundations of strong-field phenomena defines and compares regimes of field--matter interaction in periodic systems, including (perfect) crystals as well as optical and semiconductor superlattices, followed by a review of recent experimental advances in the study of strong-field dynamics in crystals and nanostructures. Avenues toward measuring and controlling electronic processes up to petahertz frequencies are discussed

Efficient and realistic device modeling from atomic detail to the nanoscale

As semiconductor devices scale to new dimensions, the materials and designs become more dependent on atomic details. NEMO5 is a nanoelectronics modeling package designed for comprehending the critical multi-scale, multi-physics phenomena through efficient computational approaches and quantitatively modeling new generations of nanoelectronic devices as well as predicting novel device architectures and phenomena. This article seeks to provide updates on the current status of the tool and new functionality, including advances in quantum transport simulations and with materials such as metals, topological insulators, and piezoelectrics.Comment: 10 pages, 12 figure

Wigner model for quantum transport in graphene

The single graphene layer is a novel material consisting of a flat monolayer of carbon atoms packed in a two-dimensional honeycomb-lattice, in which the electron dynamics is governed by the Dirac equation. A pseudo-spin phase-space approach based on the Wigner-Weyl formalism is used to describe the transport of electrons in graphene including quantum effects. Our full-quantum mechanical representation of the particles reveals itself to be particularly close to the classical description of the particle motion. We analyze the Klein tunneling and the correction to the total current in graphene induced by this phenomenon. The equations of motion are analytically investigated and some numerical tests are presented. The temporal evolution of the electron-hole pairs in the presence of an external electric field and a rigid potential step is investigated. The connection of our formalism with the Barry-phase approach is also discussed