No abstract

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.

The non-equilibrium Green's function (NEGF) method with Büttiker probe scattering self-energies is assessed by comparing its predictions for the thermal boundary resistance with molecular dynamics (MD) simulations. For simplicity, the interface of Si/heavy-Si is considered, where heavy-Si differs from Si only in the mass value. With Büttiker probe scattering parameters tuned against MD in homogeneous Si, the NEGF-predicted thermal boundary resistance quantitatively agrees with MD for wide mass ratios. Artificial resistances that plagued NEGF calculations in homogeneous systems so far are absent in the present NEGF approach. Spectral transport information result from NEGF without transformations in its natural representation. The spectral results show that the scattering between different phonon modes plays a crucial role in thermal transport across interfaces.Semiconductor nanodevices such as quantum cascade lasers, LEDs and thermoelectric devices are typically composed of several semiconductor materials 1-4 . Scattering of thermal energy carriers at the interface between two materials results in thermal boundary resistance 5 . The size of the thermal boundary resistance was previously reported 6 to be comparable to that of pure materials with lengths of a few to tens of nanometers. Predicting the thermal boundary resistance gives important insight into the device physics and enables design improvements. Often, molecular dynamics (MD) is used to model the thermal boundary resistance and reproduce experimental data 7 . Inelastic phonon scattering is included in MD simulations through the anharmonicity of the interatomic potential 8 . The non-equilibrium Green's function (NEGF) method 9 is widely accepted as one of the most consistent methods for electronic quantum transport in nanodevices 10,11 . In particular for predicting stationary device physics, NEGF is potentially more attractive than MD given that it is a spectral approach when setup in energy space. When electrons and phonons are both solved in the NEGF framework, interparticle interactions and energy and momentum transfer in e.g. self-heating or thermoelectric situations can be described on equal footing with the predictions of the respective particles' propagation 12 . For phonon transport, however, the NEGF method has been used predominantly in the coherent (harmonic) regime due to the fact that the inclusion of incoherent scattering such as phonon-phonon decay usually requires solving polarization graphs in the self-consistent Born approximation which entails a large numerical load 13 . Coherent NEGF based on the Landauer approach has been plagued by artificial interface resistances in homogeneous systems 6 .In this work, a numerically efficient method to solve phonon transport in the NEGF framework including phe- * ) These authors contributed equally to this work, email: chu72@purdue.edu nomenological phonon scattering with Büttiker probes is presented and benchmarked against MD. When solved for homogeneous systems, this NEGF method yields vanishing ...

No abstract

State of the art quantum transport models for semiconductor nanodevices attribute negative (positive) unit charges to states of the conduction (valence) band. Hybrid states that enable band-to-band tunneling are subject to interpolation that yield model dependent charge contributions. In any nanodevice structure, these models rely on device and physics specific input for the dielectric constants. This paper exemplifies the large variability of different charge interpretation models when applied to ultrathin body transistor performance predictions. To solve this modeling challenge, an electron-only band structure model is extended to atomistic quantum transport. Performance predictions of MOSFETs and tunneling FETs confirm the generality of the new model and its independence of additional screening models.