Bipolar Tunneling Research Articles

Single nanowire AlN/GaN double barrier resonant tunneling diodes with bipolar tunneling at room and cryogenic temperatures

III-N semiconductor resonant tunneling diodes (RTDs) have attracted great research interest because of their potential high speed performance. Thin film III-N RTDs are challenging due to high dislocation densities resulted from large lattice and thermal expansion coefficient mismatches to substrates. Here the authors present the growth and fabrication of AlN/GaN double barrier nanowire RTDs. The AlN/GaN double barrier nanowire RTDs show clear negative differential resistance with an onset voltage between 3.5 V and 4.5 V at both room and cryogenic temperatures. The bipolar tunneling and temperature dependent device performance suggest that the electron transport of these devices is based on resonant tunneling.

Bipolar Thermoelectric Effect in a Serially Coupled Quantum Dot System

The Seebeck coefficient (S) of a serially coupled quantum dot (SCQD) junction system is theoretically studied via a two-level Anderson model. A change of sign in S with respect to temperature is found, which arises from the competition between tunneling currents due to electrons and holes (i.e., bipolar tunneling effect). The change of sign in S implies that one can vary the equilibrium temperature to produce thermoelectric current in either the forward or reverse direction, leading to a bipolar thermoelectric effect. For the case of two parallel SCQDs, we also observe the oscillatory behavior of S with respect to temperature.

High power efficiency in Si-nc/SiO2 multilayer light emitting devices by bipolar direct tunneling

We demonstrate experimentally bipolar (electrons and holes) current injection into silicon nanocrystals in thin nanocrystalline-Si/SiO2 multilayers. These light emitting devices have power efficiency of 0.17% and turn-on voltage of 1.7 V. The high electroluminescence efficiency and low onset voltages are attributed to the radiative recombination of excitons formed by both electron and hole injection into silicon nanocrystals via the direct tunneling mechanism. To confirm the bipolar character, different devices were grown, with and without a thick silicon oxide barrier at the multilayer contact electrodes. A transition from bipolar tunneling to unipolar Fowler–Nordheim tunneling is thus observed.

Theory of electron tunneling through a scanning tunneling microscopy-tip/quantum dot junction

Electron transport properties of an isolated quantum dot sandwiched between a metallic contact and a scanning tunneling microscopy tip are theoretically investigated. Keldysh-Green’s function technique is used to calculate the tunneling current of an Anderson model with multiple energy levels. The spectral function of the quantum dot system (with arbitrary number of energy levels) embedded in a tunnel junction is derived and used to calculate the tunneling current spectra. Finally, the authors calculate the emission spectra due to the electron-hole recombination that occurs in the case of bipolar tunneling, where both electrons and holes are allowed to simultaneously tunnel into the quantum dot. The authors find dramatic changes in the emission spectra as the applied bias is varied.

Theory of charge transport in a quantum dot tunnel junction with multiple energy levels

Transport properties of nanoscale quantum dots embedded in a matrix connected with metallic electrodes are investigated theoretically. The Green's function method is used to calculate the tunneling current of an Anderson model with multiple energy levels, which is employed to model the nanoscale tunnel junction of concern. A closed form spectral function of a quantum dot or coupled dots (with arbitrary number of energy levels) embedded in a tunnel junction is derived and rigorously proved via the principle of induction. Such an expression can give an efficient and reliable way for analyzing the complicated current spectra of a quantum dot tunnel junction. Besides, it can also be applied to the coupled dots case, where the negative differential conductance due to the proximity effect is found. Finally, we investigate the case of bipolar tunneling, in which both electrons and holes are allowed to tunnel into the quantum dot, while optical emission occurs. We find dramatic changes in the emission spectra as the applied bias is varied.

S-shaped current bistability in a bipolar resonant tunneling diode

The bipolar tunneling transport through p–i–n double barrier structures has been studied by means of simultaneous electrical transport measurements and electroluminescence spectroscopy. An “inverted” hysteresis loop is observed at the onset of the first electronic resonance in the current–voltage characteristics with an electrical ON/OFF ratio of more than two orders of magnitude. Relating the different branches of the current–voltage characteristic to the space charges accumulated throughout the structure the inverted hysteresis loop is interpreted in terms of an S-shaped current bistability. The S-shaped current bistability is similar to the current driven negative differential resistivity as known for instance from thyristor action. This analogy between the bipolar double barrier structure with alloyed n-type emitter and the thyristor will be briefly discussed.

Self-consistent modeling of resonant interband tunneling in bipolar tunneling field-effect transistors

We present a model for the calculation of the tunneling current in resonant interband tunneling devices based on a transfer-Hamiltonian formalism. The model is fully self-consistent and includes electrons and both light and heavy holes. In particular, we show the viability of the bipolar tunneling field-effect transistor as a three-terminal multiple-NDR device with predicted currents reaching over 1000 A/cm/sup 2/ and theoretical peak-to-valley ratios up to 300. >

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.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Bipolar tunneling field-effect transistor: A three-terminal negative differential resistance device for high-speed applications

Carrier injection across a tunnel homojunction is suggested as a new mechanism for a high-speed three-terminal device. The novel feature is the two-dimensional homojunction tunneling within a bipolar modulation doping structure. Negative differential resistance characterized by large peak-to-valley current ratios and high transconductance is anticipated. Estimates of the relevant time constants of the tunnel structure suggest the possibility of very high frequency operation.