Dejan Jovanovic

Single and multiband modeling of quantum electron transport through layered semiconductor devices

Non-equilibrium Green function theory is formulated to meet the three main challenges of high bias quantum device modeling: self-consistent charging, incoherent and inelastic scattering, and band structure. The theory is written in a general localized orbital basis using the example of the zinc blende lattice. A Dyson equation treatment of the open system boundaries results in a tunneling formula with a generalized Fisher-Lee form for the transmission coefficient that treats injection from emitter continuum states and emitter quasi-bound states on an equal footing. Scattering is then included. Self-energies which include the effects of polar optical phonons, acoustic phonons, alloy fluctuations, interface roughness, and ionized dopants are derived. Interface roughness is modeled as a layer of alloy in which the cations of a given type cluster into islands. Two different treatments of scattering; self-consistent Born and multiple sequential scattering are formulated, described, and analyzed for numerical t...

Quantum Transport with Band‐Structure and Schottky Contacts

We describe (i) a parametrized single-band model that mimics the full-band Γ-valley non-parabolicity, (ii) a method for calculating the semi-classical and quantum electron charge with the sp3s* band-structure model, and (iii) a Schottky contact model compatible with any localized orbital band-structure model.

NEMO: general release of a new comprehensive quantum device simulator

Device simulations are essential to explore new device designs, optimize performance, and analyze the underlying physics. Nanoelectronic devices pose a new challenge in this area since conventional drift-diffusion simulators are not applicable, NEMO (NanoElectronic MOdeling) is a new quantum device simulator based on a non-equilibrium Greens function formalism that simulates a wide variety of quantum devices, including RTDs, HEMTs, HBTs, superlattices, and Esaki diodes. Here we announce the general release of NEMO as a national resource freely available to the US scientific community. We present NEMO calculations for InGaAs/AlAs and GaAs/AlAs RTD devices.

Writing Research Software in a Large Group for the NEMO Project

The nanoelectronic modeling (NEMO) program is the result of a three-year development effort involving four universities and the former Corporate Research and Development Laboratory of Texas Instruments, now Applied Research Laboratory, Raytheon TI Systems, to create a comprehensive quantum device modeling tool for layered semiconductor structures. Based on the non-equilibrium Green function formalism, it includes the effects of quantum charging, bandstructure and incoherent scattering from alloy disorder, interface roughness, acoustic phonons, and polar optical phonons. NEMO addresses the diverse needs of two different types of users: (i) the engineer/experimentalist who desires a black-box design tool and (ii) the theorist who is interested in a detailed investigation of the physics. A collection of models trade off physical content with speed and memory requirements. Access to this comprehensive theoretical framework is accommodated by a Graphical User Interface (GUI) that facilitates device prototyping and in situ data analysis. We describe a hierarchical software design that allows rapid incorporation of theory enhancements while maintaining a user-friendly GUI, thus satisfying the conflicting criteria of ease of use and ease of development. The theory and GUI modules share data structures that define the device structure, material parameters, and simulation parameters. These data structures may contain general data such as integer and real numbers, option lists, vectors, matrices and the labels for both batch and GUI operation. NEMO generates the corresponding GUI elements at run-time for display and entry of these data structures.

A Generalized Tunneling Formula for Quantum Device Modeling

The generalized tunneling formula with the simple model for the broadening in the contacts gives surprisingly good results for the majority of RTD structures. It is just as fast as the standard coherent tunneling simulators and much more versatile. It is easily generalized to multi-band and multidimensional models. The multi-band generalization of the theory and the effect of the optical potential are described.

Experimentally verified quantum device simulations based on multiband models, Hartree self-consistency, and scattering assisted charging

Accurate predictions of the I-V characteristics of Esaki diodes, resonant tunneling diodes (RTD), and resonant interband tunneling diodes (RITD) require sophisticated models of bandstructure, charging, and scattering. We present direct comparisons of experimental and simulation data based on single, two, and 10 band models and the worlds first calculation of the electrostatic potential obtained self-consistently with scattering-assisted charging. This charge results from the incoherent scattering off of alloy disorder, interface roughness, acoustic phonons and polar-optical phonons.

Resonant tunneling in InP/InGaAs lateral double barrier heterostructures

Continued down-scaling of electron devices in integrated circuits in order to achieve higher density eventually results in electron devices in which quantum effects play a significant role. These quantum effects can be exploited and used to increase the functionality of electronic devices and circuits resulting in high-density (multi-valued) logic and memory functions. The lateral resonant tunneling diode and transistor are two quantum effect devices that are well suited for this task and are also ideal for planar integration. A planar lateral double barrier heterostructure is demonstrated here for the first time. Resonances in the I-V characteristics are observed that have peak to valley current ratios as high as 3.5 at 4.2 K and are attributed to resonant tunneling in a 2D/1D/2D system. The InP substrate based device structure consists of an InP/lnGaAs/InP MODFET structure within which a lateral double barrier heterostructure, consisting of InP barriers and InGaAs well and contacts, has been integrated by etch and regrowth techniques. This demonstration opens the way for the fabrication of the lateral resonant tunneling transistor.

NON-EQUILIBRIUM GREEN’S FUNCTIONS IN SEMICONDUCTOR DEVICE MODELING

We present an overview of semiconductor device modeling using non-equilibrium Green function techniques. The various e orts and their associated goals, problems, and solutions tend to naturally divide according to the dimensionality, 1D, 2D, or 3D, of the transport which we use to classify and organize the discussion. Our current e orts are largely focused on 2D and 3D modeling. The theory and approach laid out for 1D serves as the basis for 2D and 3D.

Modeling of optically switched resonant tunneling diodes

We simulate the current-voltage characteristics of an InGaAs/AlAs resonant-tunneling diode under dark and illuminated conditions. The current is given by a tunneling formula that has been generalized to allow for quantum mechanical effects in the contacts. The optically generated carriers effect on the current-voltage characteristic is included through the use of a rate equation. This method of determining the optical response is shown to be accurate at low intensity and useful for extracting the recombination lifetime. The existing simulator shows great promise as a design tool for optical RTDs and related devices.

Functional InP/InGaAs lateral double barrier heterostructure resonant tunneling diodes by using etch and regrowth

A planar integrated lateral double barrier heterostructure resonant tunneling diode is demonstrated. Resonances in the current–voltage (I–V) characteristics are observed that have peak‐to‐valley current ratios as high as 3.5 at 4.2 K and are attributed to resonant tunneling in a two‐dimensional/one‐dimensional/two‐dimensional system. The device structure consists of a lateral double barrier heterostructure embedded in an InP/InGaAs/InP modulation‐doped field‐effect transistor structure. The lateral heterostructure uses InP barriers and an InGaAs quantum well fabricated by epitaxial etch and regrowth techniques. This device and fabrication process forms the basis for lateral resonant tunneling transistors.