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...

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

Spintronics refers commonly to phenomena in which the spin of electrons in a solid state environment plays the determining role In a more narrow sense spintronics is an emerging research field of electronics: spintronics devices are based on a spin control of electronics, or on an electrical and optical control of spin or magnetism This review presents selected themes of semiconductor spintronics, introducing important concepts in spin transport, spin injection, Silsbee-Johnson spin-charge coupling, and spindependent tunneling, as well as spin relaxation and spin dynamics The most fundamental spin-dependent nteraction in nonmagnetic semiconductors is spin-orbit coupling Depending on the crystal symmetries of the material, as well as on the structural properties of semiconductor based heterostructures, the spin-orbit coupling takes on different functional forms, giving a nice playground of effective spin-orbit Hamiltonians The effective Hamiltonians for the most relevant classes of materials and heterostructures are derived here from realistic electronic band structure descriptions Most semiconductor device systems are still theoretical concepts, waiting for experimental demonstrations A review of selected proposed, and a few demonstrated devices is presented, with detailed description of two important classes: magnetic resonant tunnel structures and bipolar magnetic diodes and transistors In most cases the presentation is of tutorial style, introducing the essential theoretical formalism at an accessible level, with case-study-like illustrations of actual experimental results, as well as with brief reviews of relevant recent achievements in the field

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Semiconductor Spintronics

The classical hydrodynamic equations can be extended to include quantum effects by incorporating the first quantum corrections These quantum corrections are $O( {\hbar ^2 } )$ The full three-dimensional quantum hydrodynamic (QHD) model is derived for the first time by a moment expansion of the Wigner–Boltzmann equation The QHD conservation laws have the same form as the classical hydrodynamic equations, but the energy density and stress tensor have additional quantum terms These quantum terms allow particles to tunnel through potential barriers and to build up in potential wellsThe three-dimensional QHD transport equations are mathematically classified as having two Schrodinger modes, two hyperbolic modes, and one parabolic mode The one-dimensional steady-state QHD equations are discretized in conservation form using the second upwind methodSimulations of a resonant tunneling diode are presented that show charge buildup in the quantum well and negative differential resistance (NDR) in the current-v

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The quantum hydrodynamic model for semiconductor devices

Many semiconductor quantum devices utilize a novel tunneling transport mechanism that allows picosecond device switching speeds The negative differential resistance characteristic of these devices, achieved due to resonant tunneling, is also ideally suited for the design of highly compact, self-latching logic circuits As a result, quantum device technology is a promising emerging alternative for high-performance very-large-scale-integration design The bistable nature of the basic logic gates implemented using resonant tunneling devices has been utilized in the development of a gate-level pipelining technique, called nanopipelining, that significantly improves the throughput and speed of pipelined systems The advent of multiple-peak resonant tunneling diodes provides a viable means for efficient design of multiple-valued circuits with decreased interconnect complexity and reduced device count as compared to multiple-valued circuits in conventional technologies This paper details various circuit design accomplishments in the area of binary and multiple-valued logic using resonant tunneling diodes (RTD's) in conjunction with high-performance III-V devices such as heterojunction bipolar transistors (HBT's) and modulation doped field-effect transistors (MODFET's) New bistable logic families using RTD+HBT and RTD+MODFET gates are described that provide a single-gate, self-latching majority function in addition to basic NAND, NOR, and inverter gates

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Digital circuit applications of resonant tunneling devices

The resonant tunneling diode (RTD) has been widely studied because of its importance in the field of nanoelectronic science and technology and its potential applications in very high speed/functionality devices and circuits. Even though much progress has been made in this regard, additional work is needed to realize the full potential of RTD's. As research on RTD's continues, we will try in this tutorial review to provide the reader with an overall and succinct picture of where we stand in this exciting field or research and to address the following questions: What makes RTD's so attractive? To what extent can RTD's be modeled for design purposes? What are the required and achievable device properties in terms of digital logic applications? To address these issues, we review the device operational principles, various modeling approaches, and major device properties. Comparisons among the various RTD physical models and major features of RTD's, resonant interband tunneling diodes, and Esaki tunnel diodes are presented. The tutorial and analysis provided in this paper may help the reader in becoming familiar with current research efforts, as well as to examine the important aspects in further RTD developments and their circuit applications.

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Resonant tunneling diodes: models and properties

We investigated the current‐voltage characteristics of the double barrier, resonant tunneling structure, using a self‐consistent method. We note the significance of the effects of band bending and buildup of space charge in the quantum well. For the peak current, our calculated results agree with the measured results very well. However, the measured valley current is much greater than the calculated values.

Self‐consistent analysis of resonant tunneling current

The effect of Si doping profile on I–V characteristics of an AlGaAs/GaAs resonant tunneling barrier (RTB) structure was studied by changing the thickness of an undoped GaAs "spacer" layer placed adjacent to the RTB. We found that the peak and the valley current density in the negative differential resistance region at 77 K depends strongly on the thickness of the spacer layer. By using a spacer layer of 50 A, we achieved a resonant tunneling diode with the highest peak current density of 2×104 A/cm2 with a good peak-to-valley ratio of 3.5 at 77 K.

Effect of Silicon Doping Profile on I-V Characteristics of an AlGaAs/GaAs Resonant Tunneling Barrier Structure Grown by MBE

Light electron effective mass was found to be a very important parameter for improving the negative differential resistance (NDR) of a resonant tunneling barrier (RTB) structure. An InAlAs (41 A)/InGaAs (61.5 A)/InAlAs (41 A) RTB structure, lattice-matched to Ink, has been grown for the first time by MBE and dramatically improved NDR has been achieved. Peak current density as high as 2.2×104 A/cm2 with an excellent peak-to-valley current ratio of 11.7 was obtained at 77 K, which is the best data ever reported so far for any RTB structures.

https://iopscience.iop.org/article/10.1143/JJAP.25.L983/pdf

Excellent Negative Differential Resistance of InAlAs/InGaAs Resonant Tunneling Barrier Structures Grown by MBE

This paper reviews our current activities in hot electron transistors, and then describes recent advances in the RHET technology using InGaAs-based materials. The RHET's emitter common current gain is typically 10 to 17, with a maximum of 25, which is about four times greater than that of a GaAs-based RHET. The collector current peak-to-valley ratio reaches 19.3, with a maximum of 21.7, eight times that of the GaAs-based RHET. These are followed by theoretical and experimental analyses of the RHET's DC performance. It is found that theoretical and experimental results do not agree for the GaAs-based RHET but agree well for the InGaAs-based RHET.

Resonant-tunneling hot electron transistor (RHET)

By optimizing its structure, we have improved the current gain and collector‐current peak‐to‐valley ratio of a resonant tunneling hot‐electron transistor. The device has an asymmetric resonant tunneling barrier with an optimal well thickness to attain a higher peak‐to‐valley ratio for the collector current. Also, the device uses a graded collector barrier and decreased base thickness, exhibiting a common emitter current gain of 5.1 (at 77 K), the highest value ever reported for an AlGaAs/GaAs hot‐electron transistor.

H. Ohnishi

Papers

Self‐consistent analysis of resonant tunneling current

Effect of Silicon Doping Profile on I-V Characteristics of an AlGaAs/GaAs Resonant Tunneling Barrier Structure Grown by MBE

Excellent Negative Differential Resistance of InAlAs/InGaAs Resonant Tunneling Barrier Structures Grown by MBE

Resonant-tunneling hot electron transistor (RHET)

Resonant tunneling hot‐electron transistor with current gain of 5