The periodical-in-voltage features of the negative differential conductance (NDC) region in the current-voltage characteristics of a high-quality GaAs/AlAs terahertz resonant-tunneling diode have been detected. The found oscillations are considered taking account of the LO-phonon excitation stimulated by tunneling of electrons through the quantum active region in the resonance nanostructure where an undoped quantum well layer is sandwiched between two undoped barrier layers. Rearrangements in the I-V characteristics of the resonant-tunneling diode as a consequence of the topological transformation of a measurement circuit from the circuit with the series resistance Rs to the circuit with the shunt Rp have been experimentally studied and analyzed. The revealed substantial changes in the current-voltage characteristics of the resonant-tunneling diode are discussed schematically using Kirchhoff's voltage law.
High-frequency response properties of single and double-quantum-well resonant tunneling diodes (RTD) are examined in a wide frequency range, up to terahertz (THz) frequencies, on the base of proposed quantum theory. Numerical solutions of time-dependent Schrödinger equations with open-system boundary conditions in an external electromagnetic field are performed. The numerical solutions take into account the influence of bias DC voltage on electronic states in RTD with finite height and width of barriers both for monoenergetic and for Fermi-distributed electrons in emitter and collector parts of structures. We show that the presence of an additional level in double-quantum-well structures breaks the response symmetry and leads to selective narrow-band frequency amplification, as well as to the effect of amplification frequency tuning at THz frequencies by variation of applied bias voltage. These phenomena predict an increase of gain coefficient and open new perspectives for engineering of novel types of THz oscillators and other high-frequency units.
Development of physical principles of THz-wave amplification and oscillation is one of problems determining progress in modern solid state electronics towards high frequencies and ultrahigh performance. Novel perspectives are tied with use of resonant tunneling quantum effects, characterized by transient times less than 1 ps, comparable with fast response of superconducting devices. The information about these properties can be obtained from investigation of high-frequency oscillations or current-voltage switching phenomena in resonant-tunneling (RTD) nanostructures. In the paper the results of theoretical and experimental studies of high-frequency properties of RTD elements in subterahertz and terahertz frequency range are presented basing on developed theory of high-frequency response in RTD as well as on experimental high-frequency investigation data and current-voltage switching phenomena investigation results of effects correspondingly related to stationary current characteristics changes in single-quantum-well as well as in doublequantum- well resonant-tunneling diode nanostructures under external electromagnetic electrical field.
Resonant tunneling diode high-frequency study on the base of proposed quantum models and numerical solution of timedependent
Schrödinger equation with open-system boundary conditions in external electromagnetic field are performed
for single-quantum well and double-quantum well resonant tunneling structures. As shown the presence of privileged
additional level in double-quantum well structures breaks response symmetry, leads to narrow-band frequency selective
amplification at frequencies equal to energy spacing between levels in neighbouring quantum wells and to selection of
portion of emitter electrons that actively interact with external THz electromagnetic field. The phenomenon results in
essentially increase of gain coefficient and opens the possibility of narrow-band amplification frequency tuning in
TBRTS in THz range by variation of applied bias voltage.
Multi quantum-well long-period structures are promising for a number of important applications including the far infrared intersubband-transition-based narrow-band radiation devices, microwave resonant-tunneling and self-sustained current oscillation generators, multilevel-logic element devices based on the recently found switching effect between the multistable current states, terahertz emission detectors. All devices have in common the operation dependence on resonant-tunneling rearrangement effects in the long-period structure. We present the results of optical investigation of
resonant-tunneling rearrangement processes in long-period GaAs/AlGaAs superlattice structures under application of vertical electric field by means of low-temperature photoluminescence (PL) technique in comparisons with the data of vertical transport measurements performed simultaneously on the same structures. The effect of appearance of the new PL peaks accompanied by suppression of the old ones with increasing bias voltage has been detected, resulting from the Stark shift phenomenon. PL intensity dependences on the applied voltage are presented for the first time which complement the measured current-voltage data. The transition effect from bound (exciton) to free (electron and hole) states in electric field is observed. It is shown that the optical research method can be more sensitive in some situations to provide the crucial information about the resonant-tunneling rearrangement effects even under condition when the ordinary current-voltage measurements do not reveal any features.
Photoluminescence technique is developed for characterization of resonant-tunneling diode structures formed of the GaAs/AlGaAs long-period superlattices in process of fabrication, which allows to estimate quality of the fabricated structure after the main stages of the technological process, including the MBE growth of multi-layer structure, lithography and annealing. The long-period multiquantum-well structures are promising for development of a new kind of solid-state intersubband-transition devices emitting the narrow band radiation in far infrared. This PL technique permits the corrections of the technology parameters to grow the structures with required properties and high homogeneity and can be used at room temperature as well as at low temperature.
Microwave oscillations have been observed for the first time from the spacer-cladded GaAs/AlAs multiple-quantum-well resonant tunneling structures stabilized by a microstrip resonator system, which is compatible with use of MBE technology methods, provides a proper circuit conditions at high frequencies appearing to be rather promising for applications in millimeter and submillimeter wavelength range.
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