Heating and cooling of a two-dimensional electron gas by terahertz radiation

The absorption of terahertz radiation by free charge carriers in n-type semiconductor quantum wells accompanied by the interaction of electrons with acoustic and optical phonons is studied. It is shown that intrasubband optical transitions can cause both heating and cooling of the electron gas. The cooling of charge carriers occurs in a certain temperature and radiation frequency region where light is most efficiently absorbed due to intrasubband transitions with emission of optical phonons. In GaAs quantum wells, the optical cooling of electrons occurs most efficiently at liquid nitrogen temperatures, while cooling is possible even at room temperature in GaN heterostructures.     

Exchange interaction of S state ions with charge carriers in SnTe

ESR investigations of Mn, Eu and Gd in highly degenerate SnTe - a p-type semiconductor with metallic behaviour - prove the existence of an exchange interaction between localized magnetic moments and charge carriers. The ratio of the exchange parameters J_Mn and J_Eu between charge carriers and Mn or Eu ions, respectively, amounts to |J_Mn/J_Eu| = 8 ± 1.5. The consequence this result has on long range spin-spin interaction via charge carriers as well as on hyperfine interaction is discussed.     

Small-signal surface photoemf in semiconductor MIS-structures

Calculation of the small-signal surface photoemf in MIS-structures has been performed. By assuming that under illumination the charge of the near-surface region of the semiconductor is constant, for the surface photoemf a simple formula is derived where the power of the incident light and the semiconductor parameters enter explicitly. It follows from the obtained expression for the limiting frequency of the photoemf signal that the surface photoemf is highly sluggish because of charging and discharging of the capacity of the surface-close region with light-produced carriers. The small-signal surface photoemf has been measured in MIS-structure samples of n-and p-type silicon. Results of the calculation and experiment are in good agreement.     

Photoelectrolysis of water with semiconductors

The use of semiconductors, as photoelectrodes in electrolytic cells for the electrolysis of water, is described and the results reported in the literature for various semiconductors are reviewed. The most important properties of the semiconductor are shown to be the band-gap energyE _g , and the flat-band potentialU _fb . The semiconductor absorbs photons that are more energetic than the band-gap energy and creates electronhole pairs. These charge carriers can be separated before recombination by the electric field at the semiconductor-electrolyte interface. For electrolysis to proceed, the potential corresponding to the band gap must appreciably exceed the standard potential for the electrolysis of water, 1.23 volts. In addition, the flat-band potential must be more negative than the hydrogen potential or an external bias voltage is required. The semiconductor must not corrode under the operating conditions and must permit transfer of the minority carrier to the electrolyte. The current theories of charge transfer and reaction mechanism are discussed. Many semiconductive oxides have been tested as photoanodes and found to be stable. However, only those compounds that have band gaps of ca. 3 eV have been found to have flat-band potentials that are more negative than the hydrogen potential. These compounds will electrolyse water, without additional bias voltage, but are inefficient absorbers of solar energy. Experiments withp-type photocathodes,p andn combinations and various special configurations are also described. The paper concludes with a general discussion of the practical prospects of photoelectrolysis in comparison with solid-state solar cells.     

Heating of magnons by hot charge carriers and electrical properties of HgCr2Se4

Strong variations of the conductivity and the Hall coefficient as a function of the magnetic and electric field strengths are discovered in the ferromagnetic semiconductor HgCr₂Se₄. The nature of these phenomena is discussed in connection with its electronic structure and the strong interaction between the electric and magnetic subsystems in this magnetic semiconductor. The results can be interpreted within a model of ordinary semiconductors with consideration of the strong electron-magnon interaction specific to magnetic semiconductors, the heating of magnons by hot charge carriers, and the trapping of charge carriers (the formation of ferrons) due to the s-d exchange interaction. Fiz. Tverd. Tela (St. Petersburg) 39, 664–667 (April 1997)     

Coherent spin dynamics of electrons and excitons in nanostructures (a review)

The studies of spin phenomena in semiconductor low-dimensional systems have grown into the rapidly developing area of the condensed matter physics: spintronics. The most urgent problems in this area, both fundamental and applied, are the creation of charge carrier spin polarization and its detection, as well as electron spin control by nonmagnetic methods. Here, we present a review of recent achievements in the studies of spin dynamics of electrons, holes, and their complexes in the pump-probe method. The microscopic mechanisms of spin orientation of charge carriers and their complexes by short circularly polarized optical pulses and the formation processes of the spin signals of Faraday and Kerr rotation of the probe pulse polarization plane as well as induced ellipticity are discussed. A special attention is paid to the comparison of theoretical concepts with experimental data obtained on the n-type quantum well and quantum dot array samples.     

Deformation of germanium under the joint action of an electric current and a magnetic field

The specific features in the behavior of deformation characteristics of low-ohmic p-type germanium single crystals subjected to different types of combined plastic deformation and the anisotropy of the electrical resistance of specimens in the longitudinal and transverse directions have been investigated. Both the acceptor and donor actions of dislocations have been observed in the motion of charge carriers along the direction of compression of the specimen. Under conditions of the joint action of a weak magnetic field and a combined plastic deformation, a decrease in the macroplasticity effects has been revealed. Anisotropy of the electrical resistance of p-Ge specimens in the longitudinal and transverse directions has been found. A possible explanation of the observed effect is given.     

Charge effects in a metal-semiconductor composite system

Small-sized metallic particles contained as inclusions in an n-type nondegenerate semiconductor are considered. The problem concerning the potential and charge distributions in this composite system is analyzed in the case where regions depleted in carriers are formed around particles due to contact phenomena and these regions substantially overlap one another. The redistribution of charges among very small metallic particles (R ～ 1–10 nm) is described with due regard for the semiconductor properties of the medium and the volume fraction of particles.     

Effect of a charge layer on the plasmon-polariton dispersion curve in doped semiconductor superlattices

We consider the effects of a charge layer (accumulation and depletion layers) on the spectrum of collective plasmon-polariton modes of a semiconductor superlattice consisting of alternating mediaA andB, where mediumA is an-doped semiconductor and mediumB an insulator. The effect of the charge layer is taken into account assuming a linear position dependence for the free-carrier concentration and for the dielectric function, within mediumA. Applications are made considering mediumA asn-type semiconductor and mediumB being vacuum. We compare our results with those obtained in the abscence of the charge layer and we discuss their differences.     

Parametric interaction of space-charge waves in thin-film semiconductor structures

The general theory of parametric coupling between space-charge waves and drifting charge carriers in thin-film semiconductor structures has been worked out. This theory is applicable, in particular, to n-GaAs and n-InP semiconductors with negative differential conductance due to intervalley electron transitions under high electric fields. We started from the electrodynamic theory of waveguide excitation by extraneous currents, which was extended for arbitrary waveguide structures with composite active media. Our theory makes it possible to study parametric interaction between space-charge waves in semiconductor films with regard for boundary conditions, diffusion, the anisotropy and the frequency dispersion of the differential electron mobility, as well as the multifrequency and multimode nature of a wave process in thin-film structures.     

Capacitance-voltage characteristic of mis structures with allowance for depletion

In the ideal MIS structure considered, then-type semiconductor is uniformly doped. Allowance is made for the fact that the minority carriers in the space-charge region are in a nonequilibrium state when a high-frequency measuring signal is applied to the MIS structure. An expression is obtained for the high-frequency capacitance with allowance for depletion. It is shown that the partial ionization of the impurities must be taken into account over a wide range of donor densities. The high-frequency capacitance-voltage characteristic has been observed to have a minimum in the inversion mode. An expression is presented for the analytical determination of the minimum capacitance in the inversion mode. At donor densities higher than 10¹⁶ cm⁻³ the capacitance-voltage characteristic displays a maximum near the potential of flat bands; the maximum is due to the contribution of the charge transfer of donor levels to the high-frequency capacitance. Tomsk State Academy of Control Systems and Radio Engineering. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 24–29, May, 1996.     

Interactions between Surface Impurities and the Electron–Hole System of a Semiconductor Crystal

The effects of creation and annihilation of impurities on the surface of a highly doped semiconductor under changes in the surface concentration n of dopant atoms constituting impurities are predicted theoretically. The effects are determined by electrostatic interactions of charged surface impurity species with charge carriers and semiconductor ions. The effects are observed in a certain range of n, provided the surface impurities exhibit donor (acceptor) properties, and the semiconductor is doped with an acceptor (donor) impurity.     

Excitation of intrinsic defects in ionic crystals by high-power optical and electron beams

The efficiency of excitation and recharging of intrinsic defects by hot charge carriers has been investigated in ionic crystals acted on by high-power optical and electron beams. The interaction cross sections of hot electrons and holes with intrinsic lattice sites and F _n -type defects (n=1,2) are shown to be commensurate. It is also shown that the potential of the intracrystalline field in the vicinity of F and F ₂ centers is nearly regular. Fiz. Tverd. Tela (St. Petersburg) 40, 1030–1035 (June 1998)     

Acousto-optic amplitude modulation and demodulation of electromagnetic wave in magnetised diffusive semiconductors

Using hydrodynamical model of semiconductor plasma analytical investigations are made for the amplitude modulation as well as demodulation of an electromagnetic wave in a transversely magnetised acousto-optic semiconducting plasma. The inclusion of carriers diffusion adds new dimension in the analysis presented here. Analysis are made under different wave number regions over a wide range of cyclotron frequency. It has been seen that diffusion of charge carriers modifies amplitude modulation and demodulation processes effectively. Numerical estimations are made for n-InSb crystal irradiated by pump wave of frequency 1.6 T s^-1. Complete absorption of the waves takes place in all the possible wave lengths regimes when the cyclotron frequency becomes exactly equal to (v ² + )^1/2. Received 28 February 2002 Published online 19 July 2002     

Getter formation in silicon by implantation of antimony ions

A porous silicon layer as a getter of uncontrolled impurities has been prepared by implantation of Sb⁺ into silicon and subsequent thermal treatments. The lifetime of nonequilibrium charge carriers in n- and p-type silicon wafers with a getter layer is 3–4 times longer than that without a getter.     

InSe electrical characterization by means of transport parameters

SCLC measurements in single crystals of the layered semiconductor n-type InSe are reported. The measurements were carried out at various temperatures and on samples grown with indium added in excess (from 5 to 10%). The experimental results suggest that the trapping levels location and the charge transport are dependent on the indium excess. Only the samples grown with an indium excess of about 5% show the features typical of intrinsic semiconductors. The anomalous behaviour of samples grown with indium excess between 6 and 10 is explained by means of scattering mechanisms between charge carriers and ionized impurity centers.     

The mobility of charge carriers in a size-quantized coated semiconductor wire

Within the framework of a staircase infinitely deep potential well model, the mobility of charge carriers is calculated for scattering on impurity centers located on the axis of a size-quantized semiconducting coated wire. Calculations are done for the dielectric constant mismatch of the wire, coating and surrounding environment, taking into account the difference of the effective masses in the wire and coating. The effect of a longitudinal magnetic field on mobility is also considered. Numerical results are presented for the GaAs–Ga_1−xAl_xAs system at different values of the wire and coating radii, the alloy concentration x, and magnetic field.     

Modeling free carrier absorption in silicon

The different empirical models of light absorption in silicon by free charge carriers in near-infrared and infrared regions are analyzed. An improved empirical model for free carrier absorption in silicon is developed. Results are obtained over the wavelength range from 0.9 μm to 6 μm for n-type, and from 0.9 μm to 8 μm for p-type silicon. The new model is assessed ed by R ² parameter and the sufficient fitting of the experimental data is presented.     

Magnetic-field-induced retardation of the recombination of nonequilibrium charge carriers in semiconductors

The retardation of the recombination of electrons and holes in semiconductors in an applied uniform magnetic field has been predicted. It has been shown that the recombination time in germanium in the temperature range of T = 1–10 K at charge carrier densities of n _e = 10¹⁰−10¹⁴ cm⁻³ in magnetic fields of B = 3 × 10²−3 × 10⁴ G can be more than two orders of magnitude larger than that at zero magnetic field. This means that, after creation of nonequilibrium charge carriers by their injection at the p-n junction owing to some radiation sources or fast electron irradiation, the semiconductor retains its conductivity for a much longer time at nonzero applied magnetic field. The effect under study can be used, for example, to detect radiation sources.     

Semiconductor nanostructures modified by the UV laser radiation

The shortening of the absorption recovery time by a factor of more than 50 is observed for the semiconductor nanostructure consisting of ten GaAs/In _x Ga_1-x As/GaAs quantum wells irradiated with the nanosecond pulses of the XeCl laser.A possible reason for such a significant variation in the optical properties lies in the generation of point defects,which are responsible for recombination of charge carriers.The result can be employed in the UV photomodification of optical properties of semiconductor nanostructures.