Activation of a semiconductor surface by a pulsed magnetic field

The possibility of semiconductor surface activation, which shows up as a long-term increase in the adsorption capacity in response to a short exposure to a pulsed magnetic field, is demonstrated for the first time. Magnetic-field-induced surface activation is studied on silicon, germanium, and gallium arsenide crystals. The effect revealed extends the capabilities of thin-film growth on the semiconductor surface.     

Thermodynamic functions of electron gas on the semiconductor nanotube surface in a magnetic field

Thermodynamic functions have been calculated in the effective mass approximation for degenerate and nondegenerate electron gases on the semiconductor cylindrical nanotube surface in a longitudinal magnetic field. The Laplace transform linking the density of states and the statistical sum has been used. The thermodynamic quantities of degenerate electron gas undergo the de Haas-van Alphen oscillations with the electron Fermi energy change and the Aharonov-Bohm oscillations with the magnetic flux change within the semiconductor tube cross section. The quantities related to nondegenerate gas oscillate only with the change of magnetic flux. A peak has been found in the nondegenerate gas heat capacity-temperature diagram. A limiting process to 2D electron gas on plane has been carried out.     

Inter-subband optical absorption in an inversion layer on a semiconductor surface in magnetic fields

Lineshape of inter-subband transitions is calculated in an n-channel inversion layer on the (100) surface of Si in tilted magnetic fields. The exciton-like and the depolarization effect effect the combined subband-Landau level transition differently from the main transition. In a magnetic field parallel to the surface these effects distort the lineshape. The theory qualitatively explains the shift of the peak observed experimentally.     

Self-trapping of a wannier exciton in the optical phonon field

Stability for self-trapping of a Wannier exciton in the polarization field of optical phonons is studied by means of variational calculations based on the adiabatic approximation. The phase diagram of free and self-trapped states is presented for 1s, 2s and 2p excitons. It is shown that optical phonons can be responsible for self-trapping of 2s (2p) exciton as a trigger of self-trapping.     

Interaction between free carriers and optical field along the surface of a semiconductor material

We report an experiment showing dynamically the interaction of free carriers with an infrared wave (λ = 10.6μ) guided by the free-carrier effect (static interaction) along the surface of a semiconductor crystal (GaAs). Finally, we present as theoretical model of this experiment.     

Selective effect of a weak DC magnetic field on triglycine sulfate crystals

The effect of the selective influence of a dc magnetic field on the characteristics of nominally pure triglycine sulfate crystals was detected for the first time. A short (minutes) exposure to a weak magnetic field B₀=0.08±0.01 T caused long-term (hundreds of hours) changes in the spontaneous polarization, coercive field, Curie temperature, and permittivity of the crystal at the Curie point. The effect is selective in nature presumably because of the participation of hydrogen bond protons in the spin-dependent processes of the transformation of defect complexes in real crystals.     

Conductivity of a semiconductor superlattice in a transverse magnetic field

The conductivity of a semiconductor superlattice in a magnetic field perpendicular to the superlattice axis is calculated. The dependence of the conductivity on the magnetic field strength is studied. It is found that there is a magnetic-field range where the resistivity is proportional to the magnetic field strength.     

Tuning the optical transmission through a homogeneous doped semiconductor film by applying an external magnetic field

We theoretically and numerically studied the transmission of light through a homogeneous doped semiconductor film with a Drude tensor in the presence of an external magnetic field. The magneto-induced homogeneous metal films are found to exhibit a magneto-induced light transparency due to cyclotron resonance. In particular, the surface plasmon (SP) resonance mode of the magneto-induced metal film move to higher frequencies with increasing magnetic field, bringing about large changes in the extraordinary light transmission peaks predicted to occur in such a magneto-induced semiconductor film.     

Lasing in the far IR spectral range under femtosecond optical excitation of the InAs semiconductor in a magnetic field

Generation of a coherent electromagnetic radiation in the far IR (THz) spectral range upon excitation of a semiconductor InAs crystal by 70-fs Ti: sapphire laser pulses is studied. The effect of a magnetic field of different orientation on generation in the submillimeter-wavelength range is analyzed. Placing the crystal into the magnetic field of an optimized permanent magnet with a strength of 5 kOe aligned along the surface of the semiconductor increased the power of generated radiation by a factor of six compared with that in the absence of the field. For the average pump-laser output power of 150 mW and repetition rate of 80 MHz, the average power of the THz radiation reached 100 nW. For detection of ultrashort pulses of the THz radiation, we used, for the first time, a highly sensitive uncooled optoacoustic detector, which detected signals with a power lower than 1 nW.     

Influence of quasi-local levels on the phonon spectrum of semimetals in a strong magnetic field

The influence of quantizing magnetic field-induced quasi-local levels, due to diamagnetic impurities, on the velocity of ultrasound in semimetals is discussed.     

The effect of temperature on the nonlinear dynamics of charge in a semiconductor superlattice in the presence of a magnetic field

The space-time dynamics of electron domains in a semiconductor superlattice is studied in a tilted magnetic field with regard to the effect of temperature. It is shown that an increase in temperature substantially changes the space-time dynamics of the system. This leads to a decrease in the frequency and amplitude of oscillations of a current flowing through the semiconductor superlattice. The quenching of oscillations is observed, which is attributed to the change in the drift velocity as a function of electric-field strength under the variation of temperature.     

Electron and phonon temperature fields in bounded semiconductors in a magnetic field

The electron and phonon temperature distributions in a semiconductor sample with finite dimensions, placed in a thermostat with an arbitrary, fixed temperature profile, were studied. Heat transfer between the thermostat and the electrons and phonons through the wall is assumed to be arbitrary, while the magnetic field is assumed to be weak.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 73–78, August, 1987.     

New mechanisms of optical writing/reading in magnetic media

Optical detection of magnetic features of 0.1 μm or less in size, as well as their generation and motion due to laser shots, is described. The physical effects discovered make it possible to implement the basic functions of a memory device (writing, shift in a storage register, and reading) by purely optical means. These effects can form a basis for designing novel ultra-high-density solid-state memories with optical access and control.     

The effect of coherent optical phonon on thermal transport

Phonons are quantized lattice vibrations and the major heat carriers in most crystalline materials. We have been utilizing femtosecond phonon spectroscopy to excite and detect optical coherent phonons (CPs) in various materials. However, the impact of CPs to overall thermal transport is still unknown. In this study, we developed a small perturbation model in MD to simulate CPs and investigate the effects of CPs on thermal transport in Bi₂Te₃ at temperatures ranging from 20 to 325 K. The phonon frequency and lifetime predicted by our model agree very well with experimental results. It is found that the effective thermal transport estimated with the heat current autocorrelation function shows a great enhancement upon CP generation and extension, especially at low temperatures. Our results suggest that it is possible to manipulate thermal transport effectively with CPs.     

Dissociation of adsorbed diatomic molecules: Combined effects of the surface magnetic field,a laser and the phonon continuum

Effects of the surface magnetic field (SMF), a laser and admolecule-phonon coupling on the dissociation of adsorbed diatomic molecules are studied theoretically. It is observed that the laser photon-dressing and the SMF-splitting of the molecular states give rise to a multiwell configuration, and the dissociation rate of a particular vibrational state in this configuration is altered as compared to the gas-phase laser-induced process. The presence of the phonon continuum also affects dissociation by dampening local transition probabilities at avoided crossings. Dissociation rates as function of laser power densities for a few specific systems are derived with a phonon-free situation and also with the presence of the phonon continuum, and the extent of phonon effects are analyzed.