Interband Tunneling Structures Research Articles

Well-defined electrical properties of high-strain resonant interband tunneling structure

The GaAs/InAs high-strain resonant interband tunneling diodes (HSRITDs) have been implemented by metal organic chemical vapor deposition (MOCVD). The current–voltage characteristics of variable quantum well and barrier thickness grown on (111) GaAs substrates are investigated. Experimental results reveal that the quantum barrier and well layer will influence current–voltage properties such as the peak current density, valley current density, and peak-to-valley current ratio (PVCR). Both peak current and valley current density decrease with increasing layers width. This result also exhibits the variation of PVCR with layers width.

Multi-band Wigner function formulation of quantum transport

A Wigner function representation of multi-band quantum transport theory is developed in this Letter. The equations are derived using non-equilibrium Green's function formulation with the generalized Kadanoff–Baym ansatz and the multi-band k.p Hamiltonian including spin. The results are applied to a two-band resonant inter-band tunneling structure.

Multi-band Wigner function formulation of quantum transport

A Wigner function representation of multi-band quantum transport theory is developed in this Letter. The equations are derived using non-equilibrium Green's function formulation with the generalized Kadanoff–Baym ansatz and the multi-band k.p Hamiltonian including spin. The results are applied to a two-band resonant inter-band tunneling structure.

Time‐Domain Analysis of One‐Dimensional Quantum‐Mechanical Waves Using Bergeron Equivalent Circuits

AbstractElectron wave devices making use of the wave nature of the electron have been studied extensively. It is important to systematically understand and use the wave phenomena in a potential structure as the operating principle of these devices. In this paper, a method based on Bergeron equivalent circuits is proposed as a technique for time domain analysis of the electron wave propagation expressed by the one‐dimensional quantum‐mechanical wave equation. It is shown that by this technique the time domain analysis of the wave behavior described by the Schrödinger equation under the effective mass approximation and the two‐ and three‐band model equations can be systematically treated by nodal analysis, including boundary conditions. Also, as a boundary condition of an open system that is important in time domain analysis, an absorbing boundary condition due to a potential structure with loss is proposed. By means of the proposed technique, the time domain analysis of the incident wave packet on a GaAs/AlAs structure considering Γ − X mixing, and on a resonant interband tunneling structure is carried out and its behavior is described. © 2001 Scripta Technica, Electron Comm Jpn Pt 2, 85(1): 1–12, 2002.

Equivalent circuit representation for resonant interband tunneling structures

Electron wave devices that use quantum-mechanical waves have been actively researched. It is important to understand and to use wave phenomena in potential structures because they are the operational basis of devices. Recently, some circuit-theoretical approaches have been proposed for analyzing and designing wave phenomena in potential structures. In this paper, equivalent circuits based on two- and three-band models that describe wave phenomena in potential structures composed of various semiconductor materials are proposed. By using the proposed equivalent circuits, wave phenomena in resonant interband tunneling (RIT) structures are formulated in terms of equivalent circuits. To confirm the validity of this method, resonant tunneling phenomena are analyzed. Circuit functions and matrices, especially the impedance concept, can be effectively used for analyzing and designing wave phenomena in RIT structures. © 1998 Scripta Technica, Electron Comm Jpn Pt 2, 81(9): 1–10, 1998

Effects of inelastic scattering on resonant interband tunneling in GaSb/AlSb/InAs/GaSb/AlSb/InAs broken-gap interband tunneling structures

Effects of inelastic scattering on interband tunneling in GaSb/AlSb/InAs/GaSb/AlSb/InAs broken-gap interband tunneling have been investigated. It is found that the interband tunneling becomes the sequential tunneling dominant due to inelastic scattering, resulting in the reduced transmission peak and the broadened full-width at half maximum. With inelastic scattering, the calculated peak current density is in better agreement with the experiments. In addition, as the valley current plays an important role in the peak-to-valley current ratio, we then try to deduce the origin of the valley currents. The thermionic current components including those from GaSb collector and GaSb well are considered to estimate the peak-to-valley current ratio. It is found that the thermionic component from the GaSb well is an important contributor to the valley current. The calculated peak-to-valley current ratio exhibits a similar variation to the experiments.

Effects of inelastic scattering on interband tunneling in GaSb/AlSb/InAs/GaSb/AlSb/lnAs broken-gap interband tunneling structures

Effects of inelastic scattering on interband tunneling in GaSb/AlSb/InAs/GaSb/AlSb/InAs BGIT's are investigated. The broadening mechanisms due to inelastic scattering are incorporated into the interband tunneling theory. The transmission and reflection coefficients are calculated with the aid of a three-band model, in which the conduction, light-hole, and split-off bands are coupled with one another. It is found that the inelastic scattering lowers the transmission peak and broadens the full-width at half-maximum, resulting in the decrease of the tunneling current. The calculated tunneling current due to inelastic scattering is found to have better agreement with the experiments. In addition, as the valley current plays an important role in the peak-to-valley current ratio (PVR), we then try to deduce the origin of the valley currents. The thermionic current is included in the valley current to estimate the peak-to-valley current ratio. The thermionic component from the GaSb well has important contribution to the valley current in the studied structures. The peak-to-valley current ratio is also estimated and found to have better agreement with the experiment when the inelastic scattering is considered.

Analysis of resonant tunneling using the equivalent transmission-line model

Presents a simple general and exact method for solving resonant tunneling problems in multilayered heterostructures. This method is based on the analogy of wave propagation between the transmission line and the potential structure. By using the proposed method, it is shown that electron wave propagation can be treated as wave propagation on an equivalent circuit and that various problems can be systematically solved by using well-developed circuit functions and circuit matrixes. In particular, our equivalent circuit can be effectively used for analysis of resonant interband tunneling (RIT) structures and resonant tunneling structures including /spl Gamma/-X mixing by using the interface matrix. Various properties of the resonant tunneling structure and a guideline for designing new quantum effect devices can be easily obtained. In order to show the validity and usefulness of this method, some numerical examples of InAs-GaSb and GaAs-AlAs potential barrier structures are presented.

Magnetotunneling in interband tunnel structures

We examine the effect of in-plane magnetic fields on transport properties of InAs/GaSb/AlSb-based resonant interband tunneling (RIT) structures and barrierless resonant interband tunneling structures using the multiband k\ensuremath{\cdot}p quantum transmitting boundary method [Y. X. Liu et al., Phys. Rev. B 54, 5765 (1996)]. In interband tunnel structures with GaSb quantum wells, the primary peak found in the current-voltage characteristic is due to the coupling of InAs conduction-band electrons to quantized GaSb light-hole states, and a weaker shoulder peak typically shows up as the result of coupling to quantized GaSb heavy-hole states. We find that in-plane magnetic fields can enhance this electron-heavy-hole coupling, resulting in a more pronounced shoulder peak in the current-voltage characteristic. Qualitative agreement between our calculations and experimental data on RIT structures offers strong evidence for hole-mixing induced electron-heavy-hole coupling in interband tunnel structures.

Tunneling spectroscopy of resonant interband tunneling structures

We report the first study of a resonant interband tunneling (RIT) structure using tunneling spectroscopy. Peaks in the tunneling spectra are shown to correspond to energies of acoustic phonons in the constituent materials of the RIT. We conclude that these phonons are involved in inelastic tunneling through the structure and could play a role in determining the overall form of the current-voltage characteristic.

Effects of the doping levels on the characteristics of GaSb/AlSb/InAs/GaSb/AlSb/InAs broken-gap interband tunneling structures

The effects of conservation of in-plane momentum and doping levels on the low-temperature characteristics of GaSb/AlSb/InAs/GaSb/AlSb/InAs broken-gap interband tunneling structures are investigated. A three-band k · p model incorporating the coupling effects among electrons, heavy holes and light holes is used to calculate the tunneling current-voltage characteristics. It is found that the kink and the small peaks in the low-temperature characteristics are results of the conservation of in-plane momentum. With a 30 Å-thick InAs well, the low-temperature characteristics change from the ones with a shoulder at low doping levels to the ones with a kink at high doping levels. In addition, the peak current density decreases at high doping levels. With a 120 Å-thick InAs well, the peak current density increases with increasing doping levels. Besides, the small peaks at low and medium voltages and the main current peak become more significant at high doping levels. The detailed carrier transport can be interpreted with the tunneling factors and the conservation of the in-plane momentum.

InAs/AlSb/GaSb resonant interband tunneling diodes and Au-on-InAs/AlSb-superlattice Schottky diodes for logic circuits

Integrated resonant interband tunneling (RIT) and Schottky diode structures, based on the InAs/GaSb/AlSb heterostructure system, are demonstrated for the first time. The RIT diodes are advantageous for logic circuits due to the relatively low bias voltages (/spl sim/100 mV) required to attain peak current densities in the mid-10/sup 4/ A/cm/sup 2/ range. The use of n-type InAs/AlSb superlattices for the semiconducting side of Schottky barrier devices provides a means for tailoring the barrier height for a given circuit architecture. The monolithically integrated RIT/Schottky structure is suitable for fabrication of a complete diode logic family (AND, OR, XOR, INV).

The Low-Temperature Characteristics of GaSb/AlSb/InAs/GaSb/AlSb/InAs Broken-Gap Interband Tunneling Structures

The characteristics of GaSb/AlSb/InAs/GaSb/AlSb/InAs broken-gap interband tunneling structures are investigated. In addition to the main negative differential resistance peaks, kinks or small peaks can be clearly seen, especially at low temperature. The effects of the heavy-hole states are expected to play an important role. Here, a k \\cdotpp model incorporating the coupling effects of the heavy-hole states is used. It is found that the kinks and small peaks are the results of heavy-hole coupling. Furthermore, the electron distribution in the InAs emitter also contributes to the phenomena observed in the low-temperature characteristics.

Investigation of resonant interband tunneling structures using a three-band [formula omitted] model

A three-band k · p model (CLH model) considering realistically the coupling effects among the conduction band, light-hole band and heavy-hole band is proposed to investigate further the characteristics of the resonant interband tunneling structures. The tunneling current densities for k ‖-independent and -dependent cases are calculated for comparison. It is found that the inclusion of the k ‖ dependence is important in the discussion of the current-voltage (I–V) characteristics. The small peaks in low temperature I–V characteristics for GaSb/AlSb/InAs/GaSb/AlSb/InAs broken-gap interband tunneling (BGIT) structure with a 120 Å wide InAs well is owing to the substantial coupling between conduction band and heavy-hole band on nonzero k ‖. The effects coming from the k ‖ dependence also contribute to the rising of the first peak and the broading of the second peak in the low temperature I–V characteristics for BGIT structure with a 240 Å wide InAs well. A CLH model can interpret the particular phenomena in the I–V characteristics that cannot be explained by the two-band model, usually used in the investigation of the interband tunneling structures.

The study of [formula omitted] δ-doping resonant interband tunneling diode

The δ-doping InGaAs GaAs quantum well resonant interband tunneling diode by low pressure metal organic chemical vapor deposition has been successfully grown. The full width at half maximum of the doping profile analyzed by capacitance-voltage measurement is small. Two kinds of δ-doping resonant interband tunneling diodes were simulated in this study. One was the δn + -i-δp + resonant interband tunneling structure and the other was the δn + -i-δp + -i-δn + single barrier resonant interband tunneling structure. The simulated current-voltage characteristics exhibited the expected N-shaped negative differential resistance. The calculated peak-to-valley current ratio (PVCR) values of δn + -i-δp + and δn + -i-δp + -i-δp + structures are 6 and 5.6, respectively. The calculated PVCR value is larger than experimental PVCR values for the δn + -i-δp + structure. The PVCR values of this study are better than the published data of other authors.

Compositional and structural analysis of AlSb(As) tunneling barriers in InAs/AlSb(As)/GaSb resonant interband-tunneling structures

InAs/AlSb/GaSb/AlSb/InAs interband-tunneling structures have been analyzed with respect to the composition and structural quality of the AlSb tunneling barriers. The addition of AlAs monolayers at the interfaces between the AlSb barriers and the InAs and GaSb layers was found to result in the expected reduction in the valley current density of the resonant interband-tunneling diode. Vibrational mode Raman spectroscopy showed that the introduction of AlAs monolayers led to the formation of pseudoternary Al(SbAs) barriers, which cause the observed reduction of the valley current density. Ellipsometric measurements indicate that the structural quality of both types of barrier layers, with and without AlAs monolayers added to the interfaces, is inferior to that of thick bulklike AlSb layers. The observation of Raman scattering from a coupled hole plasmon-phonon mode indicates the formation of a hole gas in the GaSb quantum well at the center of the tunneling structure.

Effects of carrier mass differences on the I–V characteristics of resonant interband tunneling structures in the presence of parallel magnetic field

We investigate the effect of differences between the quantum well and the electrode carrier effective masses on the current–voltage characteristics of double-barrier interband tunneling structures under an applied magnetic field parallel to the current. The system is described by a two-band tight-binding Hamiltonian that incorporates electron and light-hole interaction and the current is calculated using the Keldysh nonequilibrium Green’s-function diagrammatic technique. The formalism is applied to InAs/AlSb/GaSb double-barrier structures considering either the InAs or the GaSb as the quantum well. The behavior of the I–V characteristics as a function of the magnetic-field strength is strongly influenced by the mass differences and opposite curvatures of the conduction and the valence bands. The features we obtain are quite different for InAs and GaSb. They are both also different from the more traditional magneto-tunneling results for GaAs/AlGaAs, where the electrodes and the quantum well electronic masses are equal. The behavior of the I–V characteristics with the applied magnetic field is in good qualitative agreement with available experimental data.

Phonon-assisted transmission in resonant interband tunneling devices

We demonstrate that phonon-assisted transmission may play a considerably lower role in interband tunneling structures than in intraband tunneling based devices as a result of the symmetry difference between electron and hole states. An example of current–voltage characteristics is calculated for resonant interband tunneling structure with confined electron and hole states.

Proposal of interband tunneling structures with strained layers

A type of interband tunneling structure with strained layers is proposed. InxGa1−xSb/ InxAl1−xSb/InAs/InxAl1−xSb/InxGa1−xSb strained resonant interband tunneling structures are theoretically studied by calculating current-voltage characteristics using realistic band structure and making comparisons to analogous unstrained structures. The results show that the interband tunneling windows of strained structures can be expanded by the introduction of strain in the InAs quantum-well layer. With a wider interband tunneling window, the peak current density is enhanced due to the broader tunneling transmission spectrum and higher bias required for resonant interband tunneling. The peak current density is also examined as a function of InAs well width for different InAlSb barrier widths.

Interband Tunneling Mechanisms and Effects of AlSb Center-Barrier Layer on Light Particle Coupling and Reverse I-V Characteristics of GaSb/AlSb/InAs/AlSb/GaSb/AlSb/InAs Triple-Barrier Structures

Light particle coupling-induced tunneling has been proven to contribute to the peak current density. The overlap carrier distribution combined with the transmission coefficient is utilized to interpret the interband tunneling mechanisms. The incorporation of an AlSb layer into the GaSb/InAs interface of GaSb/AlSb/InAs/GaSb/AlSb/InAs broken-gap structures results in GaSb/AlSb/InAs/AlSb/GaSb/AlSb/InAs triple-barrier interband tunneling structures, which have been demonstrated previously. The effects of the incorporated AlSb layer on the light particle coupling are theoretically investigated with the three-band model. It was found that, while incorporating the AlSb layer into the GaSb/InAs interface, the light-particle coupling at the interface becomes weaker, and the active region finally degenerates into two separate InAs and GaSb quantum wells. In addition, the AlSb center barrier also affects the reverse I-V characteristics of the triple-barrier structures, leading to a negative differential resistance in the reverse characteristics. The effect of the AlSb center barrier on the reverse I-V characteristics of the triple-barrier structure is also discussed.