Intrinsic Lattice Defects Research Articles

Tin Doping of Silicon for Controlling Oxygen Precipitation and Radiation Hardness

This paper reviews the impact of doping silicon with substitutional tin impurities on the formation of intrinsic and extrinsic lattice defects. The two major topics covered are (i) the effect on the diffusivity and aggregation/precipitation of interstitial oxygen in Czochralski (CZ) silicon and (ii) the formation of stable radiation defects in irradiated Sn-doped material. As demonstrated, the compressive stress associated with incorporating a large Sn atom on a lattice site is the basic feature governing the interactions with point defects. Consequently, Sn acts as a selective vacancy trap, while, in contrast, not affecting interstitial reactions. This leads to a reduced formation of oxygen thermal donors in n-type Si and lowers the concentration of vacancy-oxygen and divacancy centers in irradiated material. Enhanced oxygen precipitation has been noted around 750°C in p-type CZ silicon. Furthermore, specific Sn-related radiation defects are introduced, which question the use of doping with tin as a technique for substrate hardening. © 2001 The Electrochemical Society. All rights reserved.

Mechanism of injection-enhanced defect transformation in LPE GaAs structures

It has been shown that the electroluminescence variation in LEDs based on LPE GaAs:Si structures is a complex phenomenon, which is due to recombination-enhanced decomposition of the original complex defects with intrinsic defect appearance, subsequent diffusion of intrinsic defects and microprecipitate creation on final stage. A theoretical model of these processes has been created. The numerical calculation results of the kinetics of GaAs:Si LED EL variation and intrinsic defect transformation have been presented, which enabled us to estimate the recombination-enhanced efficiency of complex defect decomposition and the diffusion coefficient for intrinsic lattice defects, apparently interstitial Ga atoms, as well as to prove that the processes of this intrinsic defect diffusion in GaAs layer is not recombination-enhanced one.

Reduction of Electron‐Beam Induced Degradation by Rare Earth Doping in Y 3 ( Al , Ga ) 5 O 12 : Tb Phosphors

An introduction of Yb ions to phosphors is found to be effective in preventing the slow buildup of luminescence during electron‐beam irradiation. It was also discovered that discoloration and efficiency degradation in this class of phosphors can be reduced by doping of Yb or Eu ions. Thermoluminescence measurements show that trap states formed by the doping compete with intrinsic lattice defects in capturing free electrons, resulting in the decreased number of the electrons trapped in the color centers. This doping effect is related to the low charge‐transfer state energy of the trivalent rare earth ions described above.

Properties of p-PbTe (Ga) based diode structures

Single crystals of p-PbTe(Ga) with gallium density too low for complete compensation of uncontrollable impurities and intrinsic lattice defects and realization of Fermi level (FL) pinning were investigated for the purpose of producing diode structures In contact-[p-PbTe(Ga)]-Pt contact. It was found that the properties of the structures obtained have a number of features that distinguish them from In-[p-PbTe] Schottky barriers. The current-voltage characteristics (IVCs) of the experimental structures are not described by the standard relation of the Schottky theory not only in the region of reverse bias but also in the region of direct bias. Residual photoconductivity (PC) is observed under illumination with a thermal radiation source in the temperature range T<80 K; after the illumination is switched off, the IVCs are linear. Under constant illumination a photo-emf appears and the branches of the IVCs in the region of reverse biases rectify. The experimental results are discussed on the basis of the assumption that regions with n-type conductivity form and FL stabilizes near the nonohmic contact as a result of band bending. It has not been ruled out that n-PbTe(Ga) regions are initially present in the sample, but they are not manifested under ohmic contact conditions.

Analysis of Magnetite and related Ferrites by Means of Magnetic After-Effect-Spectra

The magnetic aftereffect (MAE) spectra of magnetite (Fe 3 O 4 ) and related spinel ferrites react most sensibly on smallest deviations of the crystal stoichiometry due to intrinsic or extrinsic lattice defects. Thus, the analysis of corresponding MAE spectra represents both an effective tool for quality control and classification of these materials and. moreover, a high-sensitive instrument for the detection and identification of respective lattice defects. The efficiency of this technique is demonstrated in the following on a series of instructive examples.

Optical-damage-resistant impurities (Mg, Zn, In, Sc) in lithium niobate

Abstract The paper reviews the results of recent studies of optical-damage-resistant LiNbO3:Me crystals, with Me standing for Mg, Zn, In, Sc. The effects of Me ions on LiNbO3 are very similar. This similarity manifests itself drastically in photorefractive, optical and nonlinear optical properties. The resemblance of these effects is due to a common influence of Me impurities on the intrinsic lattice defects NbLi.

Contribution of concerted exchange to the entropy of self-diffusion in Si.

The concerted-exchange (CE) mechanism is at present the only viable candidate for atomic exchange that does not involve intrinsic lattice defects. In order to evaluate its contribution to self-diffusion in Si, we calculate the entropy associated with CE. We include full relaxation of the energy surface through an interatomic potential and take into account the dominant contributions of vibrational modes through the harmonic approximation. This gives an entropy of 6.3${\mathit{k}}_{\mathit{B}}$, which accounts for a large portion of the experimental result (7${\mathit{k}}_{\mathit{B}}$--9${\mathit{k}}_{\mathit{B}}$). We conclude that the CE mechanism is a significant contributor to self-diffusion in Si.

Surface and bulk electrical properties of the hematite phase Fe2O3

Electrical properties of Fe2O3 were studied by using several electrical methods such as electrical conductivity, thermopower (Seebeck effect) and work function. The studies were performed at elevated temperatures (1053–1153 K) and under controlled oxygen activity (102∓105 Pa). Samples of different thickness varying between 103 nm and 1 mm were taken for the measurements of both electrical conductivity and thermopower. It has been found that the exponent of the po2 dependence resulting from the work function measurements (1/nφ) is about 1/2. Both thermopower and electrical conductivity data are well consistent with work function data for the thin film (1000 nm) of Fe2O3. The charge transport in Fe2O3 has been interpreted in terms of small polaron mechanism. Analysis of measured electrical parameters, regarding the thickness of studied specimens, indicates that the near-surface layer of Fe2O3 exhibits much higher deviation from stoichiometry than the bulk phase and resulting strong interaction between charge carriers. This effect has been interpreted in terms of segregation of intrinsic lattice defects to the surface, and presumably also to grain boundaries, of Fe2O3.

Lattice defects in rhodium and iridium trapped at111In probe atoms

The interaction of intrinsic lattice defects with111In probe atoms in the fcc metals rhodium and iridium has been studied between 293 and 1,400 K by means of the time differential perturbed angular correlation method. The lattice defects were produced either by the implantation of the probe atoms or by postirradiation with protons. In rhodium a unique defect-probe atom configuration leading to a quadrupole interaction frequencyvQ1=100(2)MHz and η=0 has been observed. The symmetry axis of the corresponding electric field gradient points into the 〈110〉 direction of the fcc lattice. The defect was interpreted as a monovacancy trapped at the probe atom in the 〈110〉 nearest neighbour position. In iridium two defects characterized byvQ1=118(2)MHz, η=0 andvQ2=228(2)MHz, η=0 have been observed. The symmetry axes of the corresponding electric field gradients point into the 〈110〉 and 〈111〉 directions and the defects were interpreted as a monovacancy in a nearest neighbour position and a relaxed divacancy, respectively.

Helium-vacancy interaction in helium-implanted gold

The migration and nucleation of helium atoms in gold has been studied between 10 and 900 K using the perturbed γ-γ angular correlation technique. Helium doping of the samples by implantation leads to the production of intrinsic lattice defects. The experiments reveal that vacancies act as nucleation centres for helium atoms. The influence of helium dose and helium implantation energy was investigated. Below 250 K, no helium mobility was observed. Above 250 K, four different helium-vacancy configurations (He mV n) with different stabilities were detected. Above 900 K the helium-vacancy configurations vanish in agreement with the results of desorption experiments.

The Identification of Lattice Defects in GaAs and AlGaAs

AbstractAnion antisite defects are the first convincingly identified intrinsic lattice defect in GaAs. Photo-EPR allowed to determine the energy levels of this double donor, with the single donor level being midgap. This level appears to be very similar to the technologically important “EL2” center in GaAs. However, various evidence indicates that EL2 is not due to ideal, undistorted antisite defects.Fermi level pinning at Schottky contacts on GaAs has been ascribed to intrinsic lattice defects. Antisite defects are a likely candidate for this process.Finally, the microscopic identity of the “DX” center in AlGaAs will be discussed. This defect has been generally identified with a complex of a donor atom and an unknown partner. A number of recent experimental observations indicate that this defect might rather be due to isolated donors, which get deep levels because of the change of bandstructure in the alloy system.

Defect Structure and Dynamics in Silicon

ABSTRACTThis paper gives a brief account of recent calculations of equilibrium configurations, formation energies, and migration energies of intrinsic lattice defects (vacancies, self-interstitials) and complexes of dopant impurities (phosphorus, aluminum) with these defects. The results have been used to provide a comprehensive interpretation of low- and high-temperature diffusion data.

Cluster calculations of the interactions of μ+ with lattice defects in Li

Using the Hartree-Fock Roothaan scheme we have carried out molecular cluster calculations to study the interaction of positive muon with host metal atoms and intrinsic lattice defects in lithium. The total ground state energies of the clusters are calculated selfconsistently for various assumed impurity-host configurations. From the minimum in the total energy curve, we are able to determine the equilibrium lattice constant, the relaxation of first near neighbors around the impurity, the binding energy of the muon to a lattice trap and the activation energy for muon diffusion. Extension of the present method to treatμ +-defect complexes in other metallic hosts are discussed.

Exoemission of Ethiopian Soils and the Endemicity of Non-Filarial Elephantiasis

Non-filarial elephantiasis is an endemic disease in the bare-footed population of Ethiopia. The distribution of this condition is linked with that of local red clay soil. Recently, thermoluminescence has been successfully used to distinguish between endemic and non-endemic soils. Intrinsic lattice defects, frozen in during cooling of volcanic material, are considered to be responsible for characteristic thermoluminescence signals. However, the biological reactivity of the absorbed soil particles will depend upon their surface properties. Exoemission has therefore been studied in samples from both endemic (5 samples) and non-endemic (4 samples) areas. All samples from endemic areas, on first heating, demonstrate an emission peak at 75 oC. Post-irradiation storage of samples in a moist atmosphere tends to decrease emissivity while wetting irreversibly reduces the response to irradiation. In an hydrated biological environment, this surface reactivity may be linked to the pathogenicity of the soil particles.

Exoemission of Ethiopian Soils and the Endemicity of Non-Filarial Elephantiasis

Non-filarial elephantiasis is an endemic disease in the bare-footed population of Ethiopia. The distribution of this condition is linked with that of local red clay soil. Recently, thermoluminescence has been successfully used to distinguish between endemic and non-endemic soils. Intrinsic lattice defects, frozen in during cooling of volcanic material, are considered to be responsible for characteristic thermoluminescence signals. However, the biological reactivity of the absorbed soil particles will depend upon their surface properties. Exoemission has therefore been studied in samples from both endemic (5 samples) and non-endemic (4 samples) areas. All samples from endemic areas, on first heating, demonstrate an emission peak at 75 oC. Post-irradiation storage of samples in a moist atmosphere tends to decrease emissivity while wetting irreversibly reduces the response to irradiation. In an hydrated biological environment, this surface reactivity may be linked to the pathogenicity of the soil particles.

Correlations between elephantiasis and thermoluminescence of volcanic soil

Abstract There is clinical evidence to link non-filarial elephantiasis with soil from alcalic type volcanoes but no other correlation between properties of the soils and endemic regions have been found. This paper reports the use of thermoluminescence to distinguish between endemic and non-endemic soils from Cameroon and Ethiopia. The grouping of soils by the form of the glow curve is simple and a correlation with clinical data is at least 90% successful. The link between the TL and volcanic soil is thought to involve intrinsic lattice defects which are frozen in during the cooling of volcanic material. These defects influence both TL and chemical, or biological reactivity. After annealing, the TL curves of endemic and non-endemic areas are very similar which confirms that intrinsic defects are the major source of their differences.

Ion implantation in insulators

Abstract The modifications of insulating materials by ion implantation can be of considerable interest for many applications. If ion implantation has considerable potential for changing the properties of insulators, only a few experiments have determined the critical parameters which are important in the behaviour of the implanted layer. As a matter of fact, the ion implantation process is, by its very nature, a non-equilibrium process and, in addition, the injection of charged particles in a lattice determines a concomitant creation of intrinsic lattice defects. These defects are associated with the nuclear part of the energy loss of the particles and sometimes with the electronic one (halide compounds). The characterization of these intrinsic defects and the knowledge of their spatial distribution in the lattice are necessary because the formation or dissolution of phases precipitated in the implanted layer are strongly influenced by point or extended defects. The main parameters which determine the charge state and site location of the implanted atoms in insulating targets are: ionicity of the chemical bond of the lattice, electronegativity, thermal or radiation enhanced diffusion processes, and intrinsic defects. For heavily implanted insulators, phase changes of compositional type can occur which can lead to strong modifications of the physical properties of the implanted layer. In order to obtain information on the relative extent of the critical parameters of chemical implantation in insulators it is necessary to combine analysis with different techniques such as, nuclear techniques, TEM, ESR, optical spectroscopy, X-ray diffraction at glancing angle, etc. To illustrate the effects of these parameters, typical experimental results obtained in implanted binary or ternary compounds are reported (alkali halides, silver halides, alkaline earth oxides or fluorides, transition metal oxides, natural minerals, etc.).

On the stability of TL traps of alumina

Thermoluminescence (TL) of heat-treated (in the temperature range 450 to 1400° C) α-Al2O3 powders have been studied by X-irradiation at room temperature (27° C). The TL patterns have indicated essentially two groups of traps; one in the range 50 to 250° C and the other in the range 200 to 450° C. Apart from other thermal stability characteristics, preferential bleaching by light in the wavelength region of 540 to 630 nm has been observed only in the case of the first group of TL traps. It is concluded that the TL phenomena in α-Al2O3 are in general controlled by trace impurities rather than intrinsic lattice defects and the TL traps of the system may be associated with a distribution of trapped holes (O−, O°) stabilized by trace impurities.

Effect of intrinsic lattice defects on excess currents of gallium arsenide tunnel diodes

Gallium arsenide tunnel diodes were irradiated with electrons of energy E = 2.0 MeV at room temperature. Secondary hump structures were observed in the region of 0.45 V and 0.65–1.1 V forward bias. The variation in the excess currents of diodes subjected to electronic bombardment is described on the basis of models including three levels; EB + 0.25 eV, EB + 0.55 eV, and EC−0.5 eV. Annealing of radiation-induced defects is shown to take place in two stages at temperatures of 140–180°C and 200–240°C. “Switching” and “memory” effects are observed when the current-voltage characteristics (CVC) of tunnel diodes are measured at liquid-nitrogen temperatures in darkness.

An EPR study of an S = 3/2 defect in CaWO4

AbstractAfter n‐irradiation of CaWO4 up to a dose of 3 × 1019 nvt a spectrum consisting of 12 narrow lines is observed. The angular variation of the spectrum shows that a centre with S = 3/2 located at four magnetically inequivalent sites in the structure is involved. The data are consistent with a spin Hamiltonian ℋ︁ = β S · g · B + S · D. · S, where g and D are noncoincident with principal values gz = 2.048, gy = 2.007, gx = 2.004, D1 = 4.32 × 10−4 cm−1, D2 = 0.31 × 10−4 cm−1 and D3 = −4.63 × 10−4 cm−1. Possible intrinsic lattice defects which might account for this spectrum are discussed.