Point Defect States Research Articles

Photoelectron spectroscopy of E′ centers in crystalline and glassy silicon dioxide

Radiation-induced E′ centers in SiO2 were studied to test the possibility of applying optically stimulated electron emission (OSEE) to the spectroscopy of excited states of point defects in dielectrics. The spectral responses of the OSEE of crystalline α quartz and silica glass irradiated by 10-MeV electrons were measured and studied. It was established that volume E′ centers in the crystalline and glassy SiO2 modifications are dominant emission-active defects. Surface E’s (1) centers were also detected in glassy SiO2. A model of the energy structure of E′ centers accounting for the absence of luminescence and taking into account the presence of two nonradiative (intracenter and ionization) relaxation channels is proposed. This model was used to explain the mechanism of photothermal decay of the E′ centers and to determine the ionization activation barriers and quantum yields of these centers. The emission, spectral, and kinetic parameters of the volume and surface E′ centers in glassy SiO2 were obtained, showing the excited states of these defects to have identical atomic configurations.

Diffusion mediated by doping and radiation-induced point defects

The growth of isotopically enriched epitaxial layers enables the preparation of material heterostructures, highly appropriate for simultaneous self- and dopant-diffusion studies. The advance in solid-state diffusion is demonstrated by experiments on the impact of dopant diffusion and proton irradiation on self-diffusion in silicon. Accurate modeling provides valuable information about the type and charge states of native point defects and the mechanisms of atomic transport. The results are compared with recent theoretical calculations. Consistencies and differences between experiment and theory are highlighted.

Boron diffusion in strained and strain-relaxed SiGe

SiGe has been utilized for aggressive CMOS technologies development recently and there are many references [M. Shima, T. Ueno, T. Kumise, H. Shido, Y. Sakuma, S. Nakamura, Symposium on VLSI Technology Technical Digest, 2002, pp. 94–95; T. Ghani, M. Armstrong, C. Auth, M. Bost, P. Charvat, G. Glass, T. Hoffmann, K. Johnson, C. Kenyon, J. Klaus, B. McIntyre, K. Mistry, A. Murthy, J. Sandford, M. Silberstein, S. Sivakumar, P. Smith, K. Zawadzki, S. Thompson, M. Bohr, International Electron Devices Meeting Technical Digest, December 2003, pp. 978–980; P. Bai, C. Auth, S. Balakrishnan, M. Bost, R. Brain, V. Chikarmane, R. Heussner, M. Hussein, J. Hwang, D. Ingerly, R. James, J. Jeong, C. Kenyon, E. Lee, S. Lee, N. Lindert, M. Liu, Z. Ma, T. Marieb, A. Murthy, R. Nagisetty, S. Natarajan, J. Neirynck, A. Ott, C. Parker, J. Sebastian, R. Shaheed, S. Sivakumar, J. Steigerwald, S. Tyagi, C. Weber, B. Woolery, A. Yeoh, K. Zhang, M. Bohr, International Electron Devices Meeting Technical Digest, December 2004, pp. 657–660] presenting the advantages brought by it. A better understanding regarding the boron diffusion behavior within and in the vicinity of SiGe is necessary to optimize the extension and the source/drain in pMOSFET. In order to achieve the goal, both effects from mechanical strain and Ge doping on boron diffusion have been investigated. However, only a few publications discuss the impacts of both. Furthermore, most researches investigate these two effects under the conditions of low boron concentration [P. Kuo, J.L. Hoyt, J.F. Gibbons, J.E. Turner, D. Lefforge, Appl. Phys. Lett. 66 (January (5)) (1995) 580–582; N.R. Zangenberg, J. Fage-Pedersen, J. Lundsgaard Hansen, A. Nylandsted Larsen, J. Appl. Phys. 94 (September (6)) (2003) 3883–3890] and high thermal budget anneal [P. Kuo, J.L. Hoyt, J.F. Gibbons, J.E. Turner, D. Lefforge, Appl. Phys. Lett. 66 (January (5)) (1995) 580–582; N.R. Zangenberg, J. Fage-Pedersen, J. Lundsgaard Hansen, A. Nylandsted Larsen, J. Appl. Phys. 94 (September (6)) (2003) 3883–3890; S. Eguchi, C.N. Chleirigh, O.O. Olubuyide, J.L. Hoyt, Appl. Phys. Lett. 84 (January (3)) (2004) 368–370] in which the equilibrium state of point defects is achieved. These are not the conditions used in aggressive CMOS technologies. Our experiment has therefore been designed to investigate boron diffusion in both strained and strain-relaxed SiGe including ultra-low energy, high concentration boron implant and spike RTA. Models are proposed and the retardation factors corresponding to Ge concentration and stress effect were successfully extracted through these experiments. This paper describes these experiments, with the calibration and the resulting diffusion constants for an ultra-shallow boron junction in SiGe that is popular in advanced CMOS technology.

Low Temperature Heat Capacity of High Purity Silica Glasses in Magnetic Field

Based on the temperature response of a relaxation type calorimeter, the heat capacity of vitreous silica has been determined between 0.35 K and 30 K and in magnetic fields up to 8 T, for several high purity glasses with different hydroxyl contents and native defects. It is found that the heat capacity of synthetic silica glasses without native defects is composed of contributions due to phonons and intrinsic low-energy excitations, which are unaffected by magnetic fields. A thermodynamically consistent description of the low-energy excitations can be given in terms of the tunneling state (TS) model. The intrinsic value of the TS density of state for vitreous silica is determined to be \(\bar P\) = 0.92 · 1045J−1m−3 and increases with increasing hydroxyl content. The superlinear temperature dependence of the heat capacity found to be valid down to 15 mK is phenomenologically described by a minimal energy splitting of Δ0,min/kB ≈ 2 mK. Magnetic contributions to the specific heat observed in Suprasil W are interpreted as excited triplet states of native point defects and have been investigated in fields up to 8 T.

Determination of effective charge states for point radiation defects in fusion ceramic materials

Point defects in fusion ceramic materials under irradiation can have an effective charge due to ionization and covalent chemical bonding. The kinetics of charged point defects in these materials is determined by their effective charge and this kinetics is completely different from non-charged point defects in metals. The experimental investigation of point defect charge states in ceramic materials is rather difficult. In this paper, a new method is proposed for the investigation of charge states of point defects in irradiated ceramic materials. This method is based on a new theoretical model and experimental observations of defect cluster formation near permanent sinks, such as grain boundaries. Previous experimental investigations show that a denuded zone is formed in irradiated ceramic materials near free surfaces and grain boundaries. The effect of an applied electric field on the formation of interstitial-type point defect clusters (dislocation loops) near grain boundaries in irradiated ceramic materials is investigated. For this purpose a new theoretical model is suggested, which takes into account the effect of an applied electric field on the denuded zone formation. It is shown that the denuded zone size depends on point defect charge and direction of applied electric field. The obtained theoretical results are compared with experimental data.

Localized states of acoustic waves in three-dimensional periodic composites with point defects

Acoustic point defect states in the three-dimensional simple-cubic arrays of water spheres embedded in a mercury host are studied. Two kinds of defects are introduced, one is a sphere defect created by changing its radius, and another is a cubic defect obtained by replacing one of the spheres with a cube. The results show that a defect band appears in the band gap of the perfect crystals. The calculations show that the defect modes are localized around the defect. The influence of the filling fraction and the geometry of the defect on the defect modes are investigated in detail.

Type and charge states of point defects in heavily As- and B-doped silicon

In order to determine the type and charge states of dominant point defects in As- and B-doped silicon, self-diffusion in doped natural Si/ 30Si/natural Si double-heterostructures has been investigated under oxidizing ambient. Enhanced self-diffusion is observed in B-doped Si, while retarded self-diffusion is observed in As-doped Si. These results indicate that single-charged Si self-interstitals (I + donors) are dominant in B-doped Si, while excess single-charged vacancies (V − acceptors) exist in As-doped Si.

Red phosphorescence properties of Mn ions in MgO–GeO2 compounds

Red phosphorescence properties on Mn ions doped MgO–GeO2 compounds, Mg4GeO6,Mg2GeO4, and MgGeO3, were investigated. The red phosphorescence was observed in MgGeO3:Mn2+. The red phosphorescence intensity of MgGeO3:Mn2+ increased withadding the MgF2 and Yb2O3. The red phosphorescence duration time of sample with a batch composition of 44 mol%-MgO, 6 mol%-MgF2, 50 mol%-GeO2, 0.1 mol%-MnO, and 0.05 mol%-Yb2O3 is approximately 30 min. The mechanism of red phosphorescence in MgGeO3:Mn2+ is discussed in terms of the relationship between valency state of manganese ions and point defects in matrix compound.© 2003 Elsevier Science Ltd. All rights reserved.

Electrical activity of dislocations and point defects of deformation origin in CdxHg1−x Te crystals

The generation of dislocations with even a relatively low density (Ndis≤107cm−2) leads to significant variations in the kinetic coefficients of CdxHg1−xTe (x=0.20–0.21) crystals. In n-type crystals, a substantial decrease in electron mobility takes place along with a marked growth in electron concentration. For p-type crystals, the transition from the activation conductivity to the metal one is observed in the low-temperature range of 4.2–40 K, as is the alternating-sign behavior of the Hall coefficient R H depending on temperature and magnetic-field strength. A dominant role in the observed modifications is played by electronic states of point defects formed during the dislocation motion rather than the dislocations themselves. The totality of the data can be explained in terms of the formation of connected channels of an opposite-type conductivity in the form of a three-dimensional dislocation network in the matrix of the main crystal.

Growth and instability of charged dislocation loops under irradiation in ceramic materials

We have investigated the physical mechanisms of the growth and stability of charged dislocation loops in ceramic materials with very strong different mass of atoms (stabilized cubic zirconia) under different energies and types of irradiation conditions: 100–1000 keV electrons, 100 keV He + and 300 keV O + ions. The anomalous formation of extended defect clusters (charged dislocation loops) has been observed by TEM under electron irradiation subsequent to ion irradiation. It is demonstrated that very strong strain field (contrast) near charged dislocation loops is formed. The dislocation loops grow up to a critical size and after then become unstable. The instability of the charged dislocation loop leads to the multiplication of dislocation loops and the formation of dislocation network near the charged dislocation loops. A theoretical model is suggested for the explanation of the growth and stability of the charged dislocation loop, taking the charge state of point defects. The calculated distribution of the modified strain field by the electrical field around the charged dislocation loops is stronger than that of noncharged dislocation loops. The obtained theoretical results for the modified strain field contrast and the critical radius of unstable charged dislocation loops are compared with observed experimental data.

Point defect states in two-dimensional phononic crystals

The point defect states of acoustic wave in the two-dimensional arrays of water cylinders with circular (square) cross section in mercury host are studied. The influence of the defect geometry on the defect band modes is investigated.

Native Point Defect States in ZnO

The native point defect states in ZnO have been calculated by using afull-potential linear muffin-tin orbital method. The results show that Znvacancy and O interstitial produce the shallow acceptor levels above thevalence band. The O vacancy produces a deep donor level, while Zn interstitialproduces a shallow donor level, both below the conduction band.The Zn interstitial is the main factor which induces the native n-typeconductivity in ZnO.

Modeling of Defect Formation in Lead Chalcogenides and Their Properties

The charge states of intrinsic point defects and the thermodynamic parameters of defect formation processes in undoped lead chalcogenides were determined. The results provide an adequate description of the transport properties of the materials as a function of synthesis temperature and partial pressures of vapor species. Earlier and present experimental data are analyzed in terms of isolated point defects using the complete electroneutrality condition and taking into consideration the high-temperature band structure of the chalcogenides. The concentrations of charge carriers and predominant defects are evaluated for partial pressures corresponding to the stoichiometry ranges of the materials studied.

Deep levels of antisite defects clusters in ZnGeP2

ABSTRACTOn the basis of the methods of pseudopotential and large unit cell the research of deep lev- els of point and cluster defects in ZnGeP2 (ZGP) was carried out. It was shown that owing to lowering of the crystal lattice symmetry localised states of point defects in the ternary compound essentially differ from such states in its binary analogue GaP. Small quasicubic antisite defects clusters reduce the value of band gap, but render weak influence on the probability of optical transitions. But both single and the cluster antisite defects cause large modifications in deep levels of another point defects closed to them. On an example of phosphorus vacancy it was shown that intensive optical transitions with small energies can appear and cause an absorption in near IR – range because of antisite defects effect.

Dislocation motion in semiconducting crystals under the influence ofelectronic perturbations

The radiation enhanced dislocation glide effect was confirmed in h-ZnO aswell as in other semiconductors, which proved further the ubiquitous nature of this effect insemiconductors. Analysis of the radiation enhanced dislocation vibrationsobserved in the same h-ZnO led us to a tentative model that the effect isbrought about by fluctuations of the charge state of point defects which exertelectrostatic forces on the charged dislocations. The hydrogen-plasma enhanceddislocation glide was studied in Ge, SiGe and GaAs in addition to the previousreports on Si. The absence of the hydrogen effect in α-dislocations inn-GaAs and in thin films of SiGe is interpreted in terms of the soliton model,the essence of which is a strong binding between kinks and hydrogens.

Defect-assisted tunneling current: A revised interpretation of scanning tunneling spectroscopy measurements

Scanning tunneling microscopy (STM) is used to study low temperature grown GaAs layers. Excess As gives rise to a high concentration of As antisites (AsGa). On these point defects, tunneling spectroscopy reveals a band of donor states. In fact, the measured tunneling current results from a pure tunneling current between the energy levels of the STM tip and the AsGa energy level Et followed by an exchange of carriers between Et and the bands or between Et and donor states of neighbor point defects. We determine the influence of both contributions on the current. We show that hopping conduction is required to explain the observation of the midgap states in tunneling spectroscopy.

Effect of a weak magnetic field on the state of structural defects and the plasticity of ionic crystals

The aim of this work is to examine the influence of a weak (on the energy scale) magnetic field on the state of dislocations and point defects in ionic crystals. It is found that complex point defects existing in a metastable state are sensitive to a magnetic field B∼1 T. The contributions are identified, and the kinetics of various types of reactions within the structural defects and between them leading to plastification of the crystals in a magnetic field are determined. The effect of light on the sensitivity of the point defects to a magnetic field is described, and the spectral characteristics of this effect are determined. A resonant effect of the combined action of a weak constant magnetic field and a high-frequency magnetic field on the dislocation mobility is found to occur when these fields satisfy the conditions of electron paramagnetic resonance.

The effect of magnetic and electric fields on the state of point defects in single-crystal NaCl

It is established that exposing crystals to a pulsed electric field with an amplitude of ∼103 kV/m creates metastable states of the point defects, while a magnetic field with an induction of 7 T causes them to relax.

Reversible and irreversible magnetic-field-induced changes in the plastic properties of NaCl crystals

It is established that a weak magnetic field with induction B∼1 T gives rise to irreversible changes in NaCl crystals without freshly introduced dislocations, while a strong magnetic field with induction 16<B<35 T gives rise predominantly to reversible changes. It is inferred that there exist two different channels whereby a magnetic field influences the state of point defects.

Self-compensation in CdTe〈Cl〉 in the presence of phase equilibrium of the system crystal-cadmium (tellurium) vapor

The self-compensation of charged point defects in CdTe〈Cl〉 is investigated down to the lower limit of free-carrier densities (ni,pi) over the entire range of vapor pressures PCd and PTe in equilibrium of the crystal-gas phases during annealing. Under conditions where PTe2 is controlled during annealing of the crystal, the electron density n is observed to increase from 107 cm−3 to 1014 cm−3 as PTe increases from Pmin to CdTe〈Te〉 saturation. This result is attributed to the formation of a TeCd antistructural defect. The appearance of TeCd in the crystal lowers the concentration of cadmium vacancies to the point that the mechanism of exact self-compensation of CdTe〈Cl〉 is disrupted, and low-resistivity n-type crystals are obtained. The data obtained on the concentration p(n) as a function of PTe2 is used to plot the total n-ni-pi dependence with the variation of PCd-PTe2, reflecting the state of point defects in CdTe〈Te〉. The procedure for annealing crystals in two-phase crystal-gas equilibrium is used to reversibly induce ni-pi inversion of the electrical conductivity of the crystal.