William R. Frensley

Realization of a three‐terminal resonant tunneling device: The bipolar quantum resonant tunneling transistor

A new three‐terminal resonant tunneling structure in which current transport is controlled by directly modulating the potential of the quantum well is proposed and demonstrated. Typical current gains of 50 at room temperature are observed.

Spatial quantization in GaAs–AlGaAs multiple quantum dots

We present results of the fabrication and investigation of totally spatially localized crystalline structures. Low temperature photoluminescence exhibits structure that is best explained by a bottleneck for hole energy loss. This bottleneck is believed to be a direct consequence of the modification of the band structure by the fabrication‐imposed potential and is believed to be the first evidence for total spatial quantization in a fabricated heterojunction system.

Quantitative simulation of a resonant tunneling diode

Quantitative simulation of an InGaAs/InAlAs resonant tunneling diode is obtained by relaxing three of the most widely employed assumptions in the simulation of quantum devices. These are the single band effective mass model (parabolic bands), Thomas-Fermi charge screening, and the Esaki-Tsu 1D integral approximation for current density. The breakdown of each of these assumptions is examined by comparing to the full quantum mechanical calculations of self-consistent quantum charge in a multiband basis explicitly including the transverse momentum.

QUANTUM DEVICE SIMULATION WITH A GENERALIZED TUNNELING FORMULA

We present device simulations based on a generalized tunneling theory. The theory is compatible with standard coherent tunneling approaches and significantly increases the variety of devices that can be simulated. Quasi‐bound and continuum states in the leads are treated on the same footing. Quantum charge self‐consistency is included in the leads and the central device region. We compare the simulated I–V characteristics with the experimental I–V characteristics for two complex quantum device structures and find good agreement.

Quantum transport calculation of the small‐signal response of a resonant tunneling diode

The linear and lowest order nonlinear response of a quantum well resonant tunneling diode is evaluated using quantum transport theory. The calculations show that the negative conductance persists up to about 5 THz, although parasitic circuit elements will limit the maximum oscillation frequency to a much lower value. The nonlinear response (rectification) remains significant to frequencies near 10 THz and shows a resonant peak near 4 THz. These calculations support the interpretation of the experimental data of T. C. L. G. Sollner, W. D. Goodhue, P. E. Tannenwald, C. D. Parker, and D. D. Peck [Appl. Phys. Lett. 43, 588 (1983)] that rectification at 2.5 THz was observed in their devices.

Prediction of semiconductor heterojunction discontinuities from bulk band structures

We present a first attempt to predict heterojunction band lineups from the bulk band structures of the participating semiconductors, without invoking free surface properties. Band structures and electrostatic potentials are calculated by a self‐consistent pseudopotential. A simple electrostatic matching scheme lines up the electrostatic potentials, and through them the band structures. Predicted lineups are in good qualitative agreement with known lineups, and even in some cases [particularly GaAs– (Al,Ga)As] in good quantitative agreement.

Full-band simulation of indirect phonon assisted tunneling in a silicon tunnel diode with delta-doped contacts

Full-band simulations of indirect, phonon assisted, interband tunneling are used to calculate the current–voltage response of a low-temperature molecular-beam-epitaxy-grown silicon tunnel diode with delta-doped contacts. Electron confinement in the contacts results in weak structure in the current–voltage characteristic. The structure is lost when finite lifetime effects are included. The approach uses the nonequilibrium Green function formalism in a second-neighbor sp3s* planar orbital basis.

Numerical evaluation of resonant states

Abstract The quantized states formed by semiconductor heterostructures are often resonant states, in the sense that they are not asymptotically confined and thus have a finite tunneling lifetime. These states may be readily located and characterized by finding the poles of a discretized single-particle Greens function. The denominator of the Greens function is constructed from the discrete Hamiltonian matrix, augmented by terms which describe transmitting boundary conditions and which thus render the operator non-Hermitian. The resonances are the complex-valued eigenvalues of this operator. The boundary terms are energy-dependent, and thus the eigenvalue problem is nonlinear. The eigenvalues are located using a combination of linear searching and Newton iteration in the complex energy plane. For one-dimensional problems, this technique is fast enough to be used in an interactive mode, and it has been incorporated into a general-purpose interactive heterostructure modeling program. Using such a program one may rapidly examine a variety of structures and bias conditions.

Pseudomorphic bipolar quantum resonant-tunneling transistor

A bipolar tunneling transistor in which ohmic contact is made to the strained p/sup +/ InGaAs quantum well of a double-barrier resonant-tunneling structure is discussed. The heterojunction transistor consists of an n-GaAs emitter and collector, undoped AlGaAs tunnel barriers, and a pseudomorphic p/sup +/ InGaAs quantum-well base. By making ohmic contact to the p-type quantum well, the hole density in the quantum-well base is used to modulate the base potential relative to the emitter and collector terminals. With control of the quantum-well potential, the tunneling current can be modulated by application of a base-to-emitter potential. The authors detail the physical and electrical characteristics of the device. It is found that the base-emitter voltages required to bias the transistor into resonance are well predicted by a self-consistent calculation of the electrostatic potential. >

Quantum transport modeling of resonant-tunneling devices

Abstract A form of quantum transport theory has been developed to model the resonant-tunneling diode and similar devices in which quantum interference effects play a significant role. The internal state of the devices is represented by the Wigner distribution function, with boundary conditions which model the effects of the electrical contacts to the device. Inelastic scattering processes are approximated by a classical Boltzmann collision operator, and the effects of different scattering processes on the device characteristics are evaluated numerically.