Inter-subband optical absorption in space-charge layers on semiconductor surfaces

The resonance energy and the lineshape of absorption for inter-subband transitions are calculated in an approximation scheme based on the density-functional formulation inn-channel accumulation and inversion layers on the (100) surface of Si. The exciton-like effect almost cancels the resonance screening (depolarization) effect found recently by Allen et al., and the resonance energy is rather close to subband energy-separation. The agreement between the theory and experiments is satisfactory both for the resonance energy and for the lineshape. The theory is applied to accumulation layers on the (111) and (110) surface, and explains characteristic change of the lineshape observed experimentally.A research fellow of the Allexander von Humboldt Foundation     

Nonlinear voltage-temperature characteristics of submicron semiconductor layers

Voltage-temperature characteristics (VTC) of current carriers in semiconductor layers that are substantially narrower than the bulk cooling length are constructed in the temperature approximation. The nature of the VTC nonlinearity is shown to crucially depend on the ratio of the bulk to the surface energy relaxation lengths of electrons. Because these lengths depend on the electron temperature, with changing external electric fields, the contributions of these surface and bulk scattering mechanisms to energy relaxation processes may vary, leading to visible changes of VTC.In conclusion, the author would like to express his gratitude to Yu. G. Gurevich for a fruitful discussion of the results of this work.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 85–90, October, 1991.     

Surface optical solitons in semiconductor quantum dot layers

A theory of optical solitons under the condition of nonlinear coherent interaction of surface TM-modes with a layer of inhomogeneously broadened semiconductor quantum dots is developed. Explicit analytical expressions for a surface soliton (2π-pulse) in the presence of single and biexciton transitions are obtained in the regime of self-induced transparency with realistic parameters which can be reached in current experiments.     

Surface optical solitons in semiconductor quantum dot layers

A theory of optical solitons under the condition of nonlinear coherent interaction of surface TM-modes with a layer of inhomogeneously broadened semiconductor quantum dots is developed. Explicit analytical expressions for a surface soliton (2π-pulse) in the presence of single and biexciton transitions are obtained in the regime of self-induced transparency with realistic parameters which can be reached in current experiments.     

Direct observation of macroscopic charge quantization

The circuit formed by a nanoscale tunnel junction in series with a capacitance and a voltage source is the building block of most multi-junction circuits of single electronics. The state of this single electron box is entirely determined by the numbern of extra electrons on the intermediate island electrode between the junction and the capacitance. We have fabricated such a system and measured the charge on the junction capacitance, which is directly related to the average value ofn, as a function of the bias voltage using a Fulton-Dolan electrometer. At low temperature, the junction charge followed thee-periodic sawtooth function expected from the theory of macroscopic charge quantization. Strikingly,e-periodic variations were also observed when the box was superconducting. The thermal rounding of the sawtooth function is well explained by a simple model, except at the lowest temperatures.     

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.     

On quantization of the uncertainty in a measurable macroscopic quantity

The present work is devoted consequences of generalization of the radar uncertainty relation. The radar uncertainty relation has been generalized by adding a deterministic but irremovable component of the wave measurement error. One of the consequences of the generalized radar uncertainty relation is that a nonzero uncertainty minimum is achieved in measuring a macroscopic quality in an optimal nonzero uncertainty interval found by local step-by-step quantization of multipliers of the radar uncertainty relation. An algorithm of minimization of the measurement uncertainty generalizes the notion of measurement understood as a unified measuring and information process including readings, calculations, and step-by-step adaptation of the parameters of a measuring instrument to the parameters of a measurable object. The value of the macroscopic quantity measured with the least uncertainty in the optimal interval is taken to be its true value. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 73–77, September, 2006.     

Influence of magnetic quantization on the effective mass in semiconductor superlattices

An attempt is made to study the effect of a quantizing magnetic field on the effective electron mass in a semiconductor superlattice at low temperatures. It is found on the basis of the tight-binding approximation, taking GaAs-Ga_1–x Al _x As an example, that the effective mass at the Fermi level depends on the magnetic quantum number due to the cosine dependence of the wave-vector in the superlattice direction. The mass also exhibits oscillatory features in the presence of magnetic quantization because of its dependence on Fermi energy which oscillates with changing magnetic field.     

Image forces near the surface of a semiconductor with a space-charge region

The potential of image forces V(x) is estimated on the basis of the proposed model of a semiconductor surface with a space-charged region. It is shown that the existence of surface regions in which the free carrier density is substantially different from the bulk concentration, exerts a considerable effect on the behaviour of V(x) and the form of the potential barrier in the external electric field.     

Anti-parallel ferroelectric domains in surface space-charge layers of BaTiO3

It is shown on simplified models of a surface space-charge layer of a single crystal of BaTiO ₃ that in the surface region, in which the direction of the electric field is opposite to the direction of spontaneous polarization inside the crystal, anti-parallel domains can exist. The dimensions of these domains are determined. The use of the results obtained is proposed for interpreting the microrelief of the etch figures and for explaining the different phases of the polarization reversal process of a single-domain single crystal of BaTiO ₃.

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BatiO₃

BaTiO₃ , , , . . BaTiO₃.

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The author would like to thank J. Kaczer, Z. Málek and V. Dvoák of the Institute of Physics, Czechoslovak Academy of Sciences, for valuable remarks on this paper and H. Havlíková for carefully carrying out the numerical calculations.     

A contribution to the theory of the space-charge region in thin semiconductor monocrystalline films

The potential distribution in films the thickness of which is equal to or smaller than the Debye length is derived from Poisson's equation under general boundary conditions. It is shown that there exist three basic forms of this distribution depending on the densities and character of charges on both surfaces, on the geometrical thickness of the thin film and on the Debye length of the semiconductor.Notation E _S 1,E _S 2 dimensionless surface field intensities - F ₁ F ₂ space-charge functions - L _D Debye length - k Boltzmann's constant - n _b bulk electron density - N _S 1,N _S 2 concentration of surface charges - p _b bulk hole density - q electron charge - T absolute temperature - thickness of thin film measured in Debye lengths - coordinate perpendicular to the surface measured in Debye lengths - ₀ permittivity of free space - _s relative permittivity of semiconductor - dimensionless potential (multiples of kT/q) - E _cb energy of bulk conduction-band edge - E _c energy of conduction-band edge - E _i energy line that runs parallel to band edges and coincides in the bulk (assumed homogeneous) withE _ib , the intrinsic Fermi level - E _v energy of valence-band edge - E _vd energy of bulk valence-band edge - V potential     

The effect of additional Si and SiGe layers on the confinement potential of GeMn diluted ferromagnetic semiconductor

In this work we analyze the spin-polarized charge density distribution in the GeMn diluted ferromagnetic semiconductors (DFS). The calculations are performed within a self-consistent k·p method, in which the exchange correlation effects in the local density approximation, as well as the strain effects due to the lattice mismatch, are taken into account. Our findings show that the extra confinement potential provided by the barriers and the variation of the Mn content in the DFS are responsible for a separation between the different spin charge densities, giving rise to higher mobility spin-polarized currents or high ferromagnetism transition temperatures systems.     

The relationship between the macroscopic properties of PECVD silicon nitride and oxynitride layers and the characteristics of their networks

Silicon nitride and oxynitride films have been deposited on silicon wafers using plasma-enhanced chemical vapour deposition. Various amounts of ammonia, silane and nitrous oxide gases were applied at fixed total gas flow and at the same deposition temperature. The dependence of the macroscopic properties of the layers such as refractive index, internal stress and etch rate on the reaction atmosphere during deposition has been demonstrated. The chemical structure of amorphous layers was studied using infrared spectroscopy. The network was found to be characterised by SiN_xO_yH_z tetrahedra, joined to each other by common corners. The characteristic vibrational bands due to species that join tetrahedral units (N(-Si≡)₃, ≡Si-N-Si≡, ≡Si-O-Si≡) and species that stop this interconnection (Si-H, N-H) were determined and discussed with reference to the corresponding species available during deposition. The analysis resulted in the determination of the relationship between the chemical structure of the network and the layer’s refractive index, internal stress and etch rate. Received: 24 July 2000 / Accepted: 30 May 2001 / Published online: 30 August 2001     

Optical absorption in surface space-charge layers of anisotropic and tilted valley systems

In n-channel accumulation and inversion layers on the (110) and (111) surface of Si, inter-subband optical transitions can be induced by infrared light incident normal to the surface. The resonance screening and exciton-like effect depend strongly on the nature of the valley degeneracy in this configuration. Examples of numerical calculation of the absorption spectrum are presented.     

The electronic structure of alkali-metal layers on semiconductor surfaces

Alkali-metal layers on semiconductor surfaces are model systems for metal-semiconductor contacts, Schottky barriers, and metallization processes. The strong decrease of the work function as a function of alkali-metal coverage is also technically made use of. Recently, however, interest in these systems is growing owing to ongoing controversial discussions about questions like: Is the adsorbate system at monolayer coverage metallic or semiconducting, and does the metallization take place in the alkali overlayer or in the top layer of the semiconductor? Is the bonding ionic or covalent? What ist the absolute coverage at saturation? What are the adsorption sites? Do all alkali metals behave similar on the same semiconductor surface? We try to answer some of the questions for Li, Na, K and Cs on Si(111)(2×1), K and Cs on Si(111)(7×7) and on GaAs(110), and Na and K on Si(100)(2×1) employing the techniques of direct and inverse photoemission.     

Experimental evidence of macroscopic spatial quantization of angular momentum in rotating helium

Simple second sound attenuation ratios in rotating helium show that in the presence of current and even in pure rotation when B_Z is non zero the vortices exhibit a macroscopic spatial quantization described by two quantum numbers l and m.     

Surface states and annihilation characteristics of positrons trapped at reconstructed semiconductor surfaces

Positron probes of the Si(1 0 0) surface that plays a fundamental role in modern science and technology are capable to non-destructively provide information that is both unique to the probe and complimentary to that extracted using other more standard techniques. This paper presents a theoretical study of positron “image-potential” surface states and annihilation characteristics of surface trapped positrons at the Si(1 0 0) surface. Calculations are performed for the reconstructed Si(1 0 0)-p(2 × 2) surface using the modified superimposed-atom method to account for discrete-lattice effects, and the results are compared with those obtained for the non-reconstructed and reconstructed Si(1 0 0)-(2 × 1) and Si(1 1 1)-(7 × 7) surfaces. The effect of orientation-dependent variations of the atomic and electron densities on localization and extent of the positron surface state wave function at the semiconductor surface is explored. The positron surface state wave function is found to extend into the Si lattice in the regions where atoms are displaced from their ideal terminated positions due to the p(2 × 2) reconstruction. Estimates of the positron binding energy and positron annihilation characteristics reveal their sensitivity to the specific atomic structure of the topmost layers of Si. The observed sensitivity of annihilation probabilities to crystal face indicates that positron spectroscopy techniques could serve as an important surface diagnostic tool capable of distinguishing different semiconductor surfaces and defining their state of reconstruction.