Asymmetric Double Barrier Resonant Tunneling Research Articles

Coherent and Phonon-assisted Tunnelling in Asymmetric Double Barrier Resonant Tunnelling Structures

We present a theory for calculating the phonon-assisted tunnelling current in asymmetric double barrier resonant tunnelling structures (DBRTS), in which all of the phonon modes including the interface modes and the confined bulk-like LO phonons and the conduction band nonparabolicity are considered. An important physical picture about coherent and phonon-assisted tunnelling is given. The coherent tunnelling current can be directly determined by both the width of the resonant level and the peak value of the transmission coecient at the resonant level. The phonon-assisted tunnelling current mainly comes from electron interaction with higher frequency interface phonons (especially the interface phonons localised at either interface of the left barrier). Phonon-assisted tunnelling makes a significant contribution to the valley current. The subband nonparabolicity strongly influences on electron?phonon scattering and current-to-voltage characteristics. A specially designed asymmetric DBRTS may have an improved performance over the symmetric DBRTS.

Asymmetric double barrier resonant tunnelling structures with improved characteristics

We present a self-consistent calculation, based on the global coherent tunnelling model, and show that structural asymmetry of double barrier resonant tunnelling structures significantly modifies the current–voltage characteristics compared to the symmetric structures. In particular, a suitably designed asymmetric structure can produce much larger peak current and absolute value of the negative differential conductivity than its commonly used symmetric counterpart.

Electron-phonon scattering in an asymmetric double barrier resonant tunneling structure

We calculate the electron-phonon scattering rate for an asymmetric double barrier resonant tunneling structure based on dielectric continuum theory, including all phonon modes, and show that interface phonons contribute much more to the scattering rate than do bulk-like LO phonons for incident energies which are approximately within an order of magnitude of the Fermi energy. The maximum scattering rate occurs for incident electron energies near the quantum well resonance. Subband nonparabolicity has a significant influence on electron-phonon scattering in these structures. We show that the relaxation time is comparable to the dwell time of electrons in the quantum well for a typical resonant tunneling structure.

Phonon scattering in novel superlattice-asymmetric double barrier resonant tunneling structure

The scattering effects (specifically LO-phonon scattering) in a 45 Å AlAs/80 Å GaAs/33 Å AlAs asymmetric double barrier resonant tunneling (ADBRT) structure with a short period GaAS/Al0.3Ga0.7As superlattice incorporated on one side of the double barrier have been studied and characterized. Enhanced levels of current conduction were produced in the ADBRT due to the superlattice miniband electron transport under forward bias. And the effect of the said superlattice on the phonon scattering phenomena exhibited by the entire device was subsequently examined. Magnetic field fan diagrams at 4.2 K under reverse bias showed a new feature at an energy of 22 meV that could be explained on the basis of previously unreported GaAs LO-phonon scattering processes from the first excited emitter level. Finally, quenching of phonon-assisted tunneling in reverse bias on decreasing the period of the superlattice was also observed.

High pressure studies of resonant tunnelling and superlattice phenomena

Hydrostatic pressure is used to investigate two types of device based upon the n-type GaAs/(AlGa)As material system: an asymmetric double barrier resonant tunnelling device and a device incorporating two superlattices separated by a single barrier. In the double barrier structure, the pressure-induced increase in Gamma -X tunnelling and scattering reduces the build-up of electronic space charge in the GaAs quantum well. This allows one to study the transition from intrinsic bistability to ordinary negative differential conductivity in I(V). In the superlattice/barrier/superlattice structure the authors have evidence for a pressure-induced decrease in the free-electron density of the heavily doped n+ contact regions due to DX centres.

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.

Inverted bistability in the current-voltage characteristics of a resonant tunneling device

The current-voltage characteristics of an asymmetric double barrier resonant tunneling device show a butterfly-shaped hysteresis loop in which, for a range of voltage, the off-resonant current exceeds the resonant current. This “inverted bistability” is due to the effects of space charge buildup in the quantum well. Magnetoquantum oscillations in the tunnel current with B | J are used to investigate the distribution of charge within the device and the intersubband scattering processes which control the charge buildup.

Investigation of asymmetric double barrier resonant tunneling structures based on (AlGa)As/GaAs

The phenomenon of bistability in resonant tunneling devices is discussed. The influence of charge build-up in the quantum well on the current-voltage characteristic is considered. It is shown that this build-up can be considerably enhanced by using a thin emitter barrier and a thick collector barrier and lead to current bistability via an electrostatic feedback process. The experimental I( V) characteristic is interpreted with the aid of data on magnetoquantum oscillation over a wide range of fields and voltage baises.