Dynamics of defects in semiconductors

Hyperfine interaction techniques involving radioactive probe atoms like the perturbed angular correlation technique (PAC) and the Mössbauer effect have, due to their inherent sensitivity, successfully been applied to the study of defects in semiconductors. By probing the characteristic charge distribution around the probe atom interacting with a defect, they contributed to the microscopic understanding of the nature, structure and stability of complexes formed between radioactive dopant atoms and defects present in elemental and compound semiconductors. Moreover, dynamic effects can be studied by hyperfine interaction probe techniques. In this case, dynamics always means the fluctuation of a charge distribution resulting in a time dependent hyperfine interaction within the time scale defined by the lifetime of the isomeric nuclear state used for the measurement. Such fluctuations can either be caused by structural changes like local rearrangements of a defect complex or by electronic transitions in the semiconductor resulting in a change of the charge state of a defect complex. Examples using PAC to monitor such processes will be discussed for the semiconductor silicon.     

A high-intensity58Co slow-positron beam and applications to probe near-surface disorder

Properties and performance of a magnetically-guided, high-intensity, ultra-high-vacuum slow-positron beam are reviewed. Basic positron behaviour in solids is briefly described. Results from various⁵⁸Co ⁺ sources in conjunction with a backscattering W(110) moderator are presented. We discuss research applications to probe depth distribution of open-volume lattice defects. Two experimental methods capable of yielding information on defects within 500 Å and 1 m from the surface, respectively, are considered. Results are shown on defect distribution in ion implanted metals and semiconductors.This paper is based on an invited talk at the International Symposium Production of Low-Energy Positrons with Accelerators and Applications Giessen, FRG, (25–27 September, 1986)     

Multi-exponential analysis of DLTS

Deep-level transient spectroscopy (DLTS), which is widely used to characterize deep impurity centers in semiconductors, assumes a single exponential wave form for the transient junction capacitance. When there are several closely spaced energy levels this assumption is no more valid, and the conventional DLTS may lead to errorneous results. To overcome this difficulty we propose here a novel method which we call the multi-exponential DLTS(MEDLTS). The transient wave form of the junction capacitance is directly analysed into multi-exponential compouents using the nonlinear least-squares analysis program DISCRETE developed by Provencher. The resolved time constants of these components are then displayed in the form of aT ²–1/T plot. According to the results of simulation with various parameters MEDLTS is shown quite effective to resolve closely spaced energy levels which can not be resolved by the conventional DLTS. As an example of the application of this method deep levels in Si: Au were investigated. The results have shown that a single peak in conventional DLTS actually consists of two adjacent levels with activation energies and capture cross-sectionsE _B1=0.49 eV, _B1=1.1×10^–14cm² andE _B2=0.46 eV, _B2=1.3×10^–15 cm² and with amplitude ratio 11.     

Finslerian N-Spinors: Algebra

New mathematical objects called Finslerian N-spinors are discussed. The Finslerian N-spinor algebra is developed. It is found that Finslerian N-spinors are associated with an N²-dimensional flat Finslerian space. A generalization of the epimorphism SL(2, ) O ₊ (1, 3) to a case of the group SL(N,) is constructed. Particular examples of Finslerian N-spinors for N = 2, 3 are considered in detail.     

Properties of electrically active structural defects in crystalline semiconductors

The internal structures, composite elements, electrophysical properties, and characteristic parameters of impurity clouds, noise supertraps, disordered domains, and stacking defects are compared in crystalline semiconductors. It is shown that the mentioned macrodefects possess common properties: They have a nucleus and an impurity atmosphere, are separated by a potential barrier, are shaped with the participation of Frenkel defects and oxygen ions, have a threshold inclusion, sharply increase the rate of charge carrier generation-recombination as the electrical field grows, etc. It is noted that current channels in non-crystalline semiconductors are characterized by properties close to these after they have been formed. It is assumed that the electrical activity of the structural macrodefects in crystalline semiconductors may be related to the fundamental properties of noncrystalline semiconductors (for instance, the resistance switching effect). Domains adjoining a macrodefect and destroyed by it visibly manifest these properties.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 95–100, April, 1988.     

Solution of coupled differential equations of soliton theory

We present the complete set of solutions of the coupled differential equations of the form ()²=(), ² =(). Equations of this form appear in several physical situations.     

Indium-defect complexes in silicon studied by perturbed angular correlation spectroscopy

The formation of molecule-like complexes, consisting of a defect and a radioactive¹¹¹In atom, is studied using the perturbed angular correlation technique (PAC). The complexes are characterized by their defect specific electric field gradients which also contain information on the geometry of the formed complexes. Whereas the complex is formed with the¹¹¹In atom, its electric field gradient is measured after the decay of the radioactive¹¹¹In atom to¹¹¹Cd. Formation and dissolution of the molecule-like complexes is pursued for a variety of different conditions, such as sample temperature, dopant concentration and position of the Fermi level. In particular, the interaction of In atoms with the following defects in Si was investigated: Intrinsic defects, created by particle irradiation; substitutional donor atoms (P, As, Sb, Bi); and interstitial impurity atoms (Li, H, and an unidentified X defect); especially, the latter ones are known to passivate acceptor atoms in Si. Methodology and specific properties of the PAC technique will be illustrated with the help of these examples.     

Long range scattering for nonlinear Schrödinger equations in one space dimension

We consider the scattering problem for the nonlinear Schrödinger equation in 1+1 dimensions: where = /x,R{0},R,p>3. We show that modified wave operators for (*) exist on a dense set of a neighborhood of zero in the Lebesgue spaceL ²(R) or in the Sobolev spaceH ¹(R)., The modified wave operators are introduced in order to control the long range nonlinearity |u|² u.Laboratoire associé au Centre National de la Recherche Scientifique     

119Sn Mössbauer study of the implantation behaviour of119In,119Sn,119mSn,119Sb and119mTe ions in SiC

The implantation behaviour of stable¹¹⁹Sn⁺ ions and radioactive¹¹⁹In⁺,^119mSn⁺,¹¹⁹Sb⁺ and^119mTe⁺ ions in SiC has been investigated by, respectively, conversion-electron Mössbauer spectroscopy on the 24 keV transition of¹¹⁹Sn, and by Mössbauer emission spectroscopy on the 24 keV radiation emitted by the¹¹⁹Sn daughter after the decays of the radioactive isotopes. The Mössbauer spectra could be decomposed in most cases into two groups of lines, one originating from¹¹⁹Sn atoms on substitutional Si sites, the other from various Sn-vacancy complexes distinguished by their Mössbauer parameters. Annealing experiments reveal a strong dependence of the structure of the defects and the formation and annealing kinetics on the chemical nature of the impurities. Defects formed in 297 K implantations with^119mSn and¹¹⁹Sb anneal above 500 C, resulting in a preferential location of the impurities on substitutional Si sites, whereas^119mTe atoms are efficient defect-trapping centres and no stable, substitutional fraction is observed on either lattice site. Possible structures for the Sn-vacancy complexes are discussed and comparison is made to similar defect complexes in group IV and in III–V semiconductors.     

Inverse Problem for a General Bounded Domain inR3 with Piecewise Smooth Mixed BoundaryConditions

We study the influence of a finite container on an ideal gas. The trace of theheat kernel (t) = _{= 1}exp(–t), where {} _{= 1}are the eigenvalues of the negative Laplacian – ² = – ³ _{= 1}(/x )² in the (x ¹, x ², x ³)-space,is studied for a general bounded domain with a smooth bounding surface S, where afinite number of Dirichlet, Neumann, and Robin boundary conditions on thepiecewise smooth parts S _i (i = 1, ..., n) of S are considered such that S =U _{i = 1} S _i . Some geometrical properties of (the volume, the surface area, the meancurvature, and the Gaussian curvature) are determined. Furthermore,thermodynamic quantities, particularly the energy, for an ideal gas enclosed inthe general bounded domain with Dirichlet, Neumann, and Robin conditionsare examined with the help of the asymptotic expansions of (t) for short timet. We show that these thermodynamic quantities depend on some geometricproperties of .     

Defect trapping by100Pd in fcc metals

Lattice defects in Al, Cu, Ag and Au were studied by the perturbed angular correlation technique (PAC) using the probe atom¹⁰⁰Pd/¹⁰⁰Rh. The comparison of data obtained on interstitial trapping in Cu and Au at different probe atoms (¹⁰⁰pd,¹¹¹In) allows defect characterisation less affected by the respective probe. The trapping efficiency of¹⁰⁰Pd for vacancy like defects is quite different to that of¹¹¹In atoms.     

ENDOR-investigations of iron doped GaAs and GaP

From ENDOR-measurements of GaAs:Fe³⁺ the symmetries and hyperfine parameters of three groups of neighbour nuclei have been obtained. The values of ||², r ^–3 and of the electric field gradients at the sites of the neighbour nuclei have been determined for GaAs:Fe³⁺ and GaP:Fe³⁺. The comparison of our results with those of NMR-investigations indicates the Fe³⁺-ion to be an interstitial impurity surrounded by four groupV atoms in a tetrahedral arrangement.     

Spectral Complex for Controlling the Parameters of the Plasmachemical‐Reactor Working Medium

An automated spectral complex for controlling the parameters of the plasmachemicalreactor working medium by the emission and absorption spectra in the 200–1100 and 2000–5000nm ranges has been developed. To record radiation, a CCD array and a pyroelectric detector are used. Control of the spectral device functions, data recording, and the obtaining of results reflecting the workingmedium parameters and the concentration in it of components being measured are carried out by means of a personal computer. The complex makes it possible to study the temporal behavior of the workingmedium parameters being measured with a resolution of up to 10^–2 sec.     

Magnetic moments of proton drip-line nuclei13O and9C

The magnetic moments of the proton drip-line nuclei¹³O(I = 3/2^–,T _1/2 = 8.6 ms) and 9C(I = 3/2^–,T _1/2 = 126 ms) have been determined for the first time through the combined techniques of polarized radioactive nuclear beams and-NMR detection. The observed magnetic moments are ¦(¹³O)¦ = 1.3891 ±0.0003 _N and ¦(⁹C)¦ = 1.3914 ±0.0005 _N. Spin expectation values are deduced to be 0.76 and 1.44 for¹³O and⁹C, respectively. While the of¹³O is consistent with the systematics from isospinT= 1/2 mirror pairs, the of⁹C is unusually large, even far larger than the single particle value, = 1.     

TypeN vacuum space-times as special functions in ℂ2

The members of one explicit class of functions in ² are identified with the geodetic shear-free null congruences in Minkowski's space-time. Members of a second explicit class are identified with the type-N vacuum space-times with twist-free rays. These two classes are special subclasses from a larger class of functions associated with the type-N space-times. This larger class is characterized in the following way: If and are holomorphic variables in ², thenu (, , ), a function holomorphic in, belongs to the class provided the function u/ u satisfies the tangential Cauchy-Riemann equation for an antiholomorphic function on the 3-surface whereu (, , ) has real values.This work was supported in part by NSF grant No. MPS74-14191-A01.     

Impurity-defect configurations in ion-irradiated copper studied by the DPAC-technique with111In

The structure and dynamics of lattice defects in copper are investigated. The defects have been produced by irradiation with heavy ions of 350 keV between 85 K and 300 K. Three different defect configurations are distinguished by the time differential perturbed angular correlation technique (DPAC) with¹¹¹In as radioactive probe. Their electric quadrupole coupling constants _Q =e ² Qq _zz /h are _Q1=116(2)MHz, _Q2=181(3)MHz and _Q3=52(1)MHz. The defects characterized by _Q1 and _Q2 are observed in the temperature range of recovery stage III. The appearance of _Q3 is closely correlated with recovery stage V. The symmetry axis of the electric field gradient associated with this defect-¹¹¹In configuration points along a crystallographic 111 direction. We attribute this defect to a planar faulted loop, presumably of vacancy type. The influence of irradiating particles and dose on the defect configurations is analyzed.     

On the Conformal Side of the Penrose Limit

Motivated by the interest in understanding the role of AdS/CFT duality in the Penrose limit, whose conformal side has received so far much less attention than the corresponding string side, we construct the pp-wave limit of N=4 superconformal mechanics with the off-shell (3,4,1) multiplet. We give the superfield and the component actions, showing that the interaction part is completely fixed by symmetry. We demonstrate that for the pp-wave case the kinetic and potential terms are invariant only when taken together, as a linear combination of the two terms, provided the value of their relative coefficient is appropriately set. We explicitly show that the passing to pp-wave limit can be achieved by keeping at most quadratic nonlinearities in the action of (super)conformal mechanics.     

High-frequency sum-rules for classical relativistic plasmas in a magnetic field

High-frequency sum rules for the transverse elements of classical relativistic plasmas in a magnetic field are derived. The relativistic effect reduces the plasma mode frequency by a factor of ^–1(1 –v²/3c².     

On the ferromagnetism of thin films

In this paper the magnetic properties of ferromagnetic thin layers are studied by calculating the partition function for the magnetic system inKirkwood's approximation of the second order. The results obtained for the Curie temperature and the magnetization are in somewhat better agreement with the experiment than those obtained by Valenta.

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The author extends his thanks to the group of research workers who performed the numerical calculation of the Curie temperatures on the computer CIFA 1, as well as gratitude to Dr. l. Valenta for so kindly supplying information on the results of his investigations on the same subject.     

Spin manifolds,killing spinors and universality of the Hijazi inequality

In terms of the Dirac operator P, we introduce on any field a first-order operator D and show that the operator (–) on the spinors (=(n/4(n–1))R; dim W=n) is positive. By means of a universal formula, we show that, on a compact spin manifold of dimension 3, the Hijazi inequality [8] holds for every spinor field such that (P, P) = ²(, ) (=const.). In the limiting case, the manifold admits a Killing spinor which can be evaluated in terms of . Different properties of spin manifolds admitting Killing spinors are proved. D is nothing but the twistor operator.