Bistable cyclotron resonance in semiconductors

We consider the cyclotron resonance in a semiconductor which has a band with a relativistic energy-momentum dispersion and show that, when subject to quasi-resonant radiation, the energy of a free carrier in this band and the relative potential drop between the two surfaces of the semiconductor facing the radiation exhibit bistability under classical single electron approximation.     

Optically detected cyclotron resonance in semiconductors

In high quality semiconductor crystals, occurrence of cyclotron resonance is beautifully reflected on luminescence spectra. This feature is demonstrated in typical elemental semiconductor Ge, both doped and undoped. One obtains new information of kinetics in free carriers, free excitons, bound excitons and electron-hole drops.     

The evaluation of the effect of piezo-electric scattering on the cyclotron resonance half-width in weakly polar semiconductors

Following the method given by Srinivas et al., the scattering of electrons on acoustic phonons and its effect on the cyclotron resonance width in CdS and CdTe is calculated. Two mechanisms: scattering by means of a deformation potential and through piezo-electric coupling are considered; the importance of the latter is stressed.     

Electron-plasmon coupling in semiconductors: Harmonics of cyclotron resonance

Plasmon assisted absorption of infrared radiation leads to relatively intense absorption peaks close to harmonics of the electron cyclotron frequency for both the cyclotron resonance active and cyclotron resonance inactive circular polarizations.     

On a possibility of negative cyclotron resonance in semiconductors

A possibility of negative conductance at the cyclotron resonance frequency of hot carriers in crossed electric and magnetic fields is investigated. It relies on sufficiently strong carrier-optical phonon interaction compared with other scattering processes. The condition is examined numerically but seems to hardly be satisfied in presently available crystals.     

The influence of Landau level broadening on temperature dependent cyclotron resonance linewidths in semiconductors

The effects of Landau level broadening, due to impurity fluctuations, on cyclotron resonance linewidths in semiconductors are reported. Allowing for level broadening, a calculation of the linewidth Γ shows a rapid low temperature increase, in contrast to earlier (non-broadening) calculations which give $\text{Γ ∞ T}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$. At low temperatures the broadening of the density of states causes a strong narrowing of the linewidth. These results are in good agreement with the experimental data reported for III-V and II-VI semiconductors. The effects of electron localisation are also considered.     

Optical detection of cyclotron resonance for characterization of recombination processes in semiconductors

Novel applications of the technique of optically detected cyclotron resonance (ODCR) are discussed. This method is an extension of the conventional cyclotron resonance investigations and shows important advantages when applied to characterization of semiconductor materials. These advantages are due to a higher sensitivity and a longer momentum relaxation time caused by photoneutralization of ionized impurities. This in turn enables experiments at lower magnetic fields and lower microwave radiation frequency. Photoexcitation used in ODCR often results in a simultaneous observation of electron and hole cyclotron resonances in the same sample, which is a rare case in a conventional CR study. High magnetic field far infrared ODCR experiments utilize all these advantages of the method. For the most common X-band (10 GHz) microwave setups, the ODCR resolution often is too low to allow accurate CR determination of the band structure parameters of the material studied. In that case, ODCR may be used for high-resolution photoluminescence experiments and for identification of carrier capture and recombination paths at impurities, as was proposed recently. These new and important applications of the ODCR technique are described here, and documented by recent experimental results. The mechanism of ODCR detection for pure and doped semiconductors is discussed, and a prominent role of the impact ionization mechanism is demonstrated. This is followed by a discussion of recent applications of ODCR for identification of recombination mechanisms. Then high spectral resolution ODCR experiments are described, with the example of overlapping free-to-bound and donor-acceptor pair transitions. Some special applications of ODCR are demonstrated. ODCR also can be applied to analyze quantum confinement of carriers in two-dimensional (2D) structures such as heterojunctions and quantum wells. It is shown that useful information can be obtained on the electronic properties of the 2D electron (or hole) gas and the interlayer carrier transfer enhanced by carrier heating at CR absorption in such structures.     

Determination of oscillator strengths from the self-absorption of resonance radiation in rare gases

A method is presented which determines directly oscillator strengths for rare gas atoms from the selfabsorption of resonance radiation. It is shown that under suitable experimental conditions the oscillator strength can be derived from the selfabsorption by a simple formalism. Some problems concerning this method are treated in detail, such as reemission of absorbed radiation and the presence of more than one isotope. A value of 0.262±0.018 was obtained for the oscillator strength of the He(1¹S→2¹P) resonance transition. Preliminary data were also obtained for some resonance transitions in neon, using neon gas with a natural abundance of the isotopes.     

Hot electron population inversion and cyclotron resonance negative differential conductivity in semiconductors

The Monte-Carlo calculation is used to support the suggestion⁴ that the hot electrons in semiconductors, the spontaneous optical phonon emission being the main scattering process, may exhibit a negative differential conductivity (NDC) at the cyclotron resonance (CR). A brief discussion of the possibility of NDC at the high frequencies (ω ? 2–5 × 10¹²sec^-1) under the population inversion in n-GaAs in a strong electric field¹ is also given.     

The appearance of a d. c. electromotive force and nonuniform hall effect in semiconductors under the parametric cyclotron resonance condition

A theory of the parametric cyclotron resonance (PCR) is developed for semiconductors placed in a non-uniform magnetic field. Owing to this non-uniformity, a gradient of the mean electron energy arises in the specimen, which results in a dependence of the charge carrier density upon the coordinate. Hence, an electromotive force and non-uniform Hall field appear in the semiconductor. Analysis of the recent measurements shows that observation of these effects is quite feasible with modern experimental techniques.     

On the theory of classical cyclotron resonance line broadening in two- and three-dimensional semiconductors

A broadening of the absorption line of the classical cyclotron resonance (CR) in two- and three-dimensional semiconductors with neutral impurities of arbitrary depth is investigated. A dependence of the half-width of the classical CR line on the impurity characteristics (depth and range of the potential) is obtained in the wide range of the parameters. The broadening is studied within the Born approximation, and also at resonant and non-resonant scattering. Fundamental differences between the line broadening by neutral impurities in two- and three-dimensional semiconductors are revealed. An alternative explanation of classical experiments on electron scattering by neutral impurities (donors) is proposed.     

EAST 电子回旋共振加热效果的数值模拟和分析

为了给EAST 电子回旋共振加热物理实验提供理论依据和模拟预测,从电子热输运方程出发,运用 CRONOS 输运程序对不同等离子体和波参数下,电子回旋加热效果进行了数值模拟计算。给出不同电子回旋波功率、入射角、电子密度和纵场等参数对电子回旋加热效果的影响,预测在不同参数下,电子温度、等离子体总内能和能量约束时间的变化,分析了其原因,并与实验结果进行了初步的比较。     

Far-infrared cyclotron resonance in n-Ge

Cyclotron resonance has been performed on the conduction band of germanium using a cyanide laser at 891 GHz and a superconducting magnet of up to 110 kG. This is 2.5 times higher in frequency and 10 times higher in field than previous cyclotron resonance measurements reported for n-Ge. The effective masses do not change from their calues at lower frequencies and fields, but the scattering frequencies are 1.5 to 5 times larger. A new scattering mechansm is suggested to explain the increased scattering.     

Surface cyclotron resonance in InSb

We have studied cyclotron resonance of electrons in an inversion layer on the surface of p-type InSb. With increasing surface charge density n_s a number of distinct resonance peaks are found to appear. These are attributed to cyclotron resonance in different electric subbands. The various cyclotron masses are found to increase with n_s and with the frequency of the far-infrared laser source.     

On the effect of trapped particles in the regime of cyclotron resonance

The motion of particles in a finite amplitude wave, propagating obliquely to the homogeneous magnetostatic field is discussed. As follows from simple integral properties, in the neighbourhood of Doppler-shifted cyclotron resonance similar trapping effects appear as in a plasma without magnetostatic field. Consequences of this trapping are discussed, in particular, the possibility of a strong absorption of the wave, and the origin of stochastic instabilities caused by the perturbation of an effective trapping potential and leading to the acceleration of particles.The author is indebted to Dr. R.Klíma, Dr. J.Lacina and Dr. P.unka for interesting discussions and to Dr. .Körbel, Mrs. P.Jaroová and Mrs. A.Harmáková for numerical calculations.     

Determination of oscillator strengths from the self-absorption of resonance radiation in rare gases—II. Neon and argon

A previously developed method, based on the self-absorption of resonance radiation, is used to derive oscillator strengths for fourteen resonance transitions of neon and argon. Electron beam excitation of the atoms is used to produce the resonance radiation, which is partly absorbed in the gas between the beam and the spectrometer. A v.u.v. spectrometer is employed to record the radiation intensities as a function of gas pressure. Oscillator strengths are derived from the measurements by using a simple formalism. The influence of recoil effects (as a consequence of the excitation process) on the shape of the spectral emission lines and thereby on the transmission is checked by detailed numerical calculations. Special attention is paid to the determination of the quantities relevant in absorption measurements, i.e. the temperature, the absorption length and the number density of the atoms. The oscillator strengths obtained are compared with results from other experiments of various types (particularly forward inelastic electron scattering, for which on the whole good agreement with the present results exists) and from theoretical calculations.     

One century of cyclotron radiation

During the one century after the theoretical prediction of the cyclotron radiation, this effect was found to contribute to many phenomena in nature and now delivers the highest powers at the shortest microwaves. The author surveys the evolution of the main ideas in this field and considers some of the devices which are based on this effect     

Amplitude characteristic of cyclotron resonance

The motion of a charged particle under the combined action of a magnetostatic field and a circularly polarized electromagnetic wave of phase velocity u higher than c, the wave being aligned with the field, is studied theoretically. A nonlinear resonance curve is found. Certain integrals of motion are derived.