Resonant Tunneling Heterostructures Research Articles

Negative differential resistance due to resonant interband tunneling of holes

The current-voltage (I-V) behavior of a GaSb(p)/AlSb/InAs/AlSb/GaSb(p) resonant interband tunneling (RIT) heterostructure is analyzed experimentally and theoretically. The structure has been successfully grown on a (100)-oriented GaAs substrate by molecular-beam epitaxy, demonstrating that more exotic lattice-matched substrates (such as InAs or GaSb) are not required for RIT devices. Theoretical simulations of I-V behavior are developed, employing a two-band tight-binding model. Experimental I-V curves show pronounced negative differential resistance, with a peak-to-valley current ratio of 8.3 at 300 K. Good agreement is observed between measured and calculated peak current densities, consistent with light-hole tunneling through the confined InAs conduction-band state.

Large peak current densities in novel resonant interband tunneling heterostructures

We have observed negative differential resistance (NDR) and large peak current densities in a novel resonant interband tunneling structure grown by molecular beam epitaxy in the InAs/GaSb/AlSb material system. The structure consists of a thin AlSb barrier layer displaced from an InAs(n)/GaSp(p) interface. NDR is readily observable at room temperature with peak current densities greater than 105 A/cm2. The enhancement in peak current density relative to a structure with no AlSb barrier is consistent with the existence of a quasi-bound state in the region between the barrier and the InAs/GaAs interface. Furthermore, we demonstrate that by growing the AlSb layer on either the InAs or GaSb side of the interface, the quasi-bound state can be localized in either material.

Optical investigation of charge accumulation and bistability in an asymmetric double barrier resonant tunneling heterostructure

A photoluminescence study of an asymmetric double barrier resonant tunneling structure, exhibiting intrinsic bistability, is reported. The variation of PL linewidth with bias provides a direct signature of the charge build-up in the well which occurs during resonant tunneling. Accurate values of the charge density are deduced from the Landau level filling in PL spectra taken as a function of magnetic field.

Space charge associated with resonant tunneling.

A general formula is obtained for the electron density per unit area associated with the quasilevel in a symmetrical resonant tunneling heterostructure. The relation of this quantum-mechanical electron accumulation to the time dependence of conduction is discussed.

Small-signal impedance of GaAs-Al x Ga 1−x as resonant tunnelling heterostructures at microwave frequency

The microwave impedance of high current drivability GaAs-AlxGa1−x As resonant tunnelling heterostructures in negative differential resistance conditions is measured. Using an equivalent circuit model that accounts for the frequency variation of the impedance, circuit elements corresponding to physical phenomena present in the device are identified.

Applications of resonant-tunneling field-effect transistors

Flip-flop and frequency-doubling operations are demonstrated, using a simple circuit that combines a resistor with a three-terminal negative-resistance device. The device is a series integration of resonant-tunneling heterostructure with a field-effect transistors. Results, obtained at 77 K, are presented for two samples that were grown by metalorganic chemical vapor deposition.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Quantum transport calculation of the frequency response of resonant-tunneling heterostructure devices

The frequency response of the quantum-well resonant-tunneling diode is calculated using quantum transport theory. The state of the device is represented by the single-particle Wigner distribution function. The Wigner function is obtained by numerical solution of the Liouville equation, subject to inhomogeneous boundary conditions that represent the ohmic contacts to the device and that introduce dissipation into the model. The small-signal ac response is calculated by a perturbation expansion about the non-equilibrium steady state. The calculations indicate that both the negative conductance and nonlinear rectification persist up to the mid terahertz region, for the design studied. This is compared to the lifetime of the resonant state inferred from the width of the scattering resonance.

A small-signal equivalent-circuit model for GaAs-AlxGa1−xAs resonant tunneling heterostructures at microwave frequencies

This paper presents a study of the microwave impedance of GaAs-AlxGa1−xAs resonant tunneling heterostructures. An equivalent-circuit model is proposed that accounts for the frequency variation of the measured impedance and whose elements correspond to physical phenomena believed to be present in the device. Empirical formulas are obtained which can be used to calculate the values of the equivalent-circuit elements from the structural parameters and the dc current-voltage characteristics of the device.

Current transport mechanisms in GaAs/AlAs tunnel structures grown by metal–organic chemical vapor deposition

Elastic and inelastic tunneling processes are investigated in GaAs–AlAs–GaAs double heterojunctions grown in the [100] direction by metal–organic chemical vapor deposition (MOCVD). The AlAs quantum barriers in the heterostructures studied are doped p-type with Mg. Theoretical calculations of tunneling currents are performed and compared with experimental I–V data. It is found that for structures with thin AlAs barriers, the dominant current transport mechanism at low temperatures is tunneling through the AlAs band gap at both the Γ and X points. This is consistent with inelastic processes observable in first (dI/dV) and second (d2I/dV2) derivative spectra obtained with modulation techniques. A simple model, developed for calculating impurity-assisted tunneling currents, shows that the role of barrier impurities becomes more important as the barrier is grown thicker. Implications of some of these results for resonant tunneling heterostructures consisting of two AlAs quantum barriers separated by a GaAs quantum well are discussed. Experimental second derivative spectra showing reproducible features are also presented for these double barrier structures.

Stable and unstable current-voltage measurements of a resonant tunneling heterostructure oscillator

Microwave oscillations in double barrier GaAs-AlxGa1−xAs resonant tunneling heterostructures have been investigated. In this letter an approach is presented to obtain stable, dc current-voltage (I-V) curves by using a damped microwave circuit to prevent device oscillations which distort the measured I-V curve. Numerical calculations confirm that if oscillations are allowed while making an I-V measurement, the measured current is the sum of the stable, bias current plus the rectified component of the oscillating current. In addition, the first room-temperature high Q microwave oscillations in resonant tunneling heterostructures are reported, as opposed to relaxation oscillations previously published. At 77 K, the highest power levels and efficiencies that have been achieved to date are presented.