The presented article contains the numerical calculations of the InGaAs/AlAs resonant tunneling diode’s (RTD) response to the AC electric field of a wide range of amplitudes and frequencies. These calculations have been performed within the coherent quantum-mechanical model that is based on the solution of the time-dependent Schrödinger equation with exact open boundary conditions. It is shown that as the field amplitude increases, at high frequencies, where ħω>Γ (Γ is the width of the resonant energy level), the active current can reach high values comparable to the direct current value in resonance. This indicates the implementation of the quantum regime for RTD when radiative transitions are between quasi-energetic levels and the resonant energy level. Moreover, there is an excitement of higher quasi-energetic levels in AC electric fields, which in particular results in a slow droop of the active current as the field amplitude increases. It also results in potentially abrupt changes of the operating point position by the ħω value. This makes it possible to achieve relatively high output powers of InGaAs/AlAs RTD having an order of 105 W/cm2 at high frequencies.

Within the framework of the coherent quantum-mechanical model, which is based on the solution of the time-dependent Schrödinger equation with exact open boundary conditions, we have numerically analyzed the behavior of the InGaAs/AlAs resonant-tunneling diode (RTD) in an alternating-current electric field in the presence of spacer layers. It is shown that the interaction of the energy levels in a quantum well of the RTD, and the same in a quantum well of the emitter spacer, leads to splitting of these levels, which sharply increases the active current of RTD. In this case, the value of the active current at the finite frequencies may exceed the active current within the low-frequency limits. For RTD, heterostructure considered active current at frequency 1.77 THz takes its maximum value at the thickness of the emitter spacer equals to 6.5 nm exceeding the corresponding value in the absence of the spacer by the factor of 32. The results obtained in this paper may be useful to improve the frequency characteristics of resonant-tunneling nanostructures.

An analytic solution to the problem of current passage via an ideal insulator in the case of monopolar hole injection has been found. The current-voltage (J-V) characteristics have been obtained for the first time in a broad range of parameters (insulator length, hole concentrations at boundaries, temperature, etc.) and applied voltages. It is shown that the Mott-Gurney quadratic J-V relation is valid only in a certain interval of currents between J (1) and J (2). For J < J (1), the current linearly depends on voltage V to within V (3) terms. A new mode has been found for J > J (2), where the J-V characteristic also becomes linear because the insulator is completely filled with injected holes. The integration constants are determined in the entire range of parameters and currents. Analytic expressions for the spatial electric-field and hole-concentration distributions are derived.

An analytic solution to the problem on transient processes in a two-barrier nanostructure is found. Explicit expressions are obtained for a transient current produced by an instantly applied weak electric field. The current relaxes to a stationary state for a time ħ /Γ (Γ is the width of a resonance level), oscillating at a frequency of ξ = ɛ − ɛ R , where ɛ is the energy of electrons coming from an emitter and ɛ R is the resonance level energy. The transient current for interacting electrons is found in the quasi-classical approximation. It is shown that interaction between electrons can drastically change the transient current, especially in the presence of hysteresis of the current-voltage characteristic (CVC). Near extreme CVC values in the region of negative differential conductivity, the oscillation frequency tends to zero and becomes imaginary, compensating the decay. Thus, the transient current relaxes with very large times without oscillations. In contrast, in the case of positive differential conductivity, the oscillation frequency becomes very high, while the relaxation time remains the same, 1/Γ.

The dependence of the peak current in the I–V characteristic of a resonant tunneling diode on the emitter spacer thickness has been investigated by numerically solving the Schrödinger equation. This dependence has pronounced maxima in which the peak current greatly exceeds that in minima. The mechanism of the formation of maxima has been revealed. These maxima are caused by the overlap of the emitter spacer level and the resonant level of the quantum well. The influence of electron-electron interaction on the effect has been studied; it is shown that the interaction barely affects the peak current in the forward bias direction and somewhat decreases it in the reverse direction.

The problem of the effect of electron-electron interaction on the static and dynamic properties of a double-barrier nanostructure (resonant tunneling diode (RTD)) is studied in terms of a coherent tunneling model, which includes a set of Schrödinger and Poisson equations with open boundary conditions. Explicit analytical expressions are derived for dc and ac potentials and reduced (active and reactive) currents in the quasi-classical approximation over a wide frequency range. These expressions are used to analyze the frequency characteristics of RTD. It is shown that the interaction can radically change the form of these expressions, especially in the case of a hysteretic I-V characteristic. In this case, the active current and the ac potentials can increase sharply at both low and high frequencies. For this increase to occur, it is necessary to meet quantum regime conditions and to choose a proper working point in the I-V characteristic of RTD. The possibility of appearance of specific plasma oscillations, which can improve the high-frequency characteristics of RTD, is predicted. It is found that the active current can be comparable with the resonant dc current of RTD.

Resonant-tunneling diode (RTD) is one of the first quantum devices. In contrast to devices settled on quantum dots and quantum threads, which works only at low temperatures, RTD can works in a wide range of temperatures from liquid-helium temperature till 100 degrees C. Also, RTD has one more feature, which makes this device attractive for use in integrated circuits - high operating frequency and, as a consequence, fast response. In this work we investigated free-running lasing of RTD in quantum regime.

Results of modeling of superconductor magnetization process based on a numerical solution of the timedependent Ginsburg-Landau equations are presented. Methods of grid approximation of the equations and method of finite elements are used. Two-dimensional patterns of changes in the order parameter and supercurrent distribution in superconductors are calculated and visualized. The main results are in agreement with the well-known representations for type I and II superconductors.

Юрий Васильевич Копаев (к 70-летию со дня рождения), Алферов Ж.И., Андреев А.Ф., Асеев А.Л., Багаев С.Н., Гинзбург В.Л., Горбацевич А.А., Елесин В.Ф., Келдыш Л.В., Крохин О.Н., Максимов Е.Г., Месяц Г.А., Чаплыгин Ю.А.

Объединенная научная сессия Отделения физических наук Российской академии наук и Объединенного физического общества Российской Федерации "Отрицательная абсолютная проводимость" (27 октября 2004 г.), Елесин В.Ф., Гантмахер В.Ф., Зверев В.Н., Рыжий В.И., Дорожкин С.И.

1. Ginzburg V L, Landau L D Zh. Eksp. Teor. Fiz. 2

Объединенная научная сессия Отделения физических наук Российской академии наук и Объединенного физического общества Российской Федерации (21 апреля 2004 г.), Пашкин Ю.А., Астафьев О.В., Ямамото Т., Накамура Й., Цай Ж.С., Жарков Г.Ф., Елесин В.Ф., Капаев В.В., Копаев Ю.В., Бараш Ю.С., Бобкова И.В., Копп Т., Максимов Е.Г.

The current and emitted (absorbed) power of a rf electric field in a resonant-tunneling diode are found as functions of the bias voltage and frequency of the electromagnetic field by solving numerically the nonstationary Schrodinger equation. It is shown that amplification (generation) is possible for voltages in a range substantially above the region of negative differential resistance and that the maximum frequencies are much higher than the values calculated for this region. (C) 1996 American Institute of Physics.

The effect of ion irradiation on the superconducting transition temperatureT c and resistivityρ ab (T) of YBa2Cu3O7-x films with different oxygen content (initial temperatureT c0≈90 K and 60 K) is studied experimentally. The dependenciesT c /T c0 on residual resistivityρ o are obtained in very wide range 0.2<T c /T c0 <1 andρ o μΩ·cm. The critical values ofρ o , corresponding to the vanishing of superconductivity, are found to be an order of magnitude larger then those predicted by theory ford-wave pairing. At 0.5÷0.6<T c /T c0<1 the experimental data are in close agreement with theoretical dependencies, obtained for the anisotropics-wave superconductor within the BCS-framework.

The photoconductivity of GaAs/AlxGa1−xAs (x=0,36) superlattices grown by molecular beam epitaxy have been investigated at T=77K. It was found that the photocurrent relaxes to “dark” current-volt characteristics j(V) even in the case of temporally constant sample illumination. The heating from 77 K to 293 K leads to the restoring of original light characteristics. The photocurrent dependence on time j(t) consists of several exponent with Г=5–50 c. Phenomenon was explained by re-charge of DX-centers in barriers. Peaks associated with those impurities were found in the low temperature photoluminescence spectrum.