Defects In Crystalline Silicon Research Articles

On the problem of a suitable definition of the cluster in embedded-cluster treatments of defects in crystals

The perturbed-cluster embedding scheme [J. Chem. Phys. 92, 7448 (1990)] adopts a self-consistent procedure where, at each cycle, a molecular cluster solution is calculated, and subsequently corrected for realizing its coupling to the crystalline environment. In the present work, it is shown that a proper design of the cluster is of critical importance for the scheme to work satisfactorily. Indications are given for defining clusters that are at the same time ‘‘self-satisfied,’’ and optimally fitted to the environment, so that correction terms are minimized. The procedure is tested in the case of defects in crystalline silicon.

Interaction between Copper and Irradiation-Induced Defects in Crystalline Silicon

Interaction between Copper and Irradiation-Induced Defects in Crystalline Silicon

A Study of Extended Defects in Silicon Crystals After Exposure to a Hydrogen Plasma

ABSTRACTThe distribution, number density, and nature of extended defects in crystalline silicon which is exposed to plasma-generated atomic hydrogen at a temperature of 250°C are characterized by transmission electron microscopy. Cross-sectional and plan-view modes are used for these characterizations. Extended defects are typically detected in the near surface region of a < 001 > crystal and their number density may exceed 109 defects-cm2, depending on die plasma exposure time, wafer temperature, gas pressure, and power. These defects exhibit contrast features which are characteristic of small dislocation loops (> 50nm in dia) and the nature of their associated strain field is assessed by diffraction-contrast techniques. The relationship between loop-like contrast features and die so-called hydrogen-induced platelet is established by both diffraction-contrast and phase-contrast imaging techniques. The results show that loop-like and platelet-like images exhibit contrast features which are consistent with a compressive strain field and therefore it is concluded that the extended defects in this study are interstitial in nature.

Electron paramagnetic resonance of hydrogen in silicon

A review of the investigations by means of electron paramagnetic resonance (EPR) of hydrogen and hydrogen-related defects in crystalline silicon is presented. The main features of the EPR center Si-AA9 (bond-centered hydrogen), which is known as the hydrogenic analogue of the anomalous muonium (Mu∗) in silicon, are discussed. It was found that the process of annealing the AA9 center is characterized by an activation energy, E = 0.48 ± 0.04 eV with a second-order pre-exponential factor, K0 = (1.25 ± 2.5) × 10-7 cm3/s.A detailed investigation by EPR of the defect (Si-AA1), which we identify as the hydrogen-related shallow donor in a positive charge state, is also presented. In particular it is shown that the H-related shallow donor is a helium-like center and its wave function has C2v symmetry. Moreover, the main features of the series of EPR spectra in silicon characteristic for the implantation of hydrogen are presented.

Defects in Crystalline Silicon - History and Outlook

Defects in Crystalline Silicon - History and Outlook

Initial applications of the molecular model to compute defect vibrations of oxygen in silicon

Abstract We have employed the molecular model introduced first by Jaswal to compute the vibrational spectra of oxygen bearing defects in a silicon crystal. This was done in the context of a silicon molecular cluster with outer valencies terminated by hydrogen. We employ the MINDO/3 semi-empirical electronic structure method to compute the total energy of the molecular cluster. We examine the conditions in applications of the molecular model required for accurate predictions of oxygen local-mode vibrational frequencies. We find that the oxygen atom and its nearest neighbor silicon atoms must be allowed to vibrate. The nearest-neighbor and next nearest-neighbor shells of silicon atoms must be allowed to relax from their lattice positions. The outermost relaxed shell of silicon atoms should be bonded to silicon atoms in their lattice positions. We apply the molecular model to three defects of crystalline silicon; interstitial oxygen, oxygen in a vacancy (the A-center), and two oxygen atoms in a vacancy. Comparison of our computed local-mode oxygen vibration frequencies with experiment shows the computed oxygen local-mode frequencies to be almost uniformly 10% greater than those observed. Isotope shifts fit experiment equally well. We conclude that the molecular model represents an accurate and efficient approach for the computation of defect local mode vibrational frequencies for oxygen and other defects in crystalline silicon.

Photothermal ionisation spectroscopy of oxygen-related shallow defects in crystalline silicon

Shallow thermal donors are electrically active oxygen-related thermally formed defects observed in oxygen-rich silicon annealed between 300 ° and 600 ° C. Seven donors have been identified with an average central-cell correction of only 5 meV. In view of their molecule-like nature this close agreement to the effective mass theory prediction for a hydrogen-like donor in silicon is of interest. It is shown that these centres are not correlated to the residual impurities phosphorus and boron but rather to the presence of nitrogen. Nitrogen-doped oxygen-rich samples show increased shallow thermal donor growth and a reduction in the growth of other oxygen-related donors in comparison to normally nitrogen-undoped oxygen-rich samples. A reduction in shallow thermal donor concentration at high nitrogen concentrations is reported.

EPR evidence of helium-oxygen-vacancy complexes in crystalline silicon

Two new ( S = 1) EPR spectra, labeled Si-AA7 and Si-AA8, arise from a helium-associated defect in crystalline silicon. Both are produced only in Czochralski-grown silicon by helium ion implantation at ≈ 20°C followed by annealing at ≈ 180°C and are stable to ≈ 350°C. The effects of stress applied at high temperature indicate an atomic reorientation process which occurs with an activation energy of 1.05 ± 0.05 eV for both centers. The Si-AA7 and Si-AA8 centers are identified as helium-related vacancy-type defects containing oxygen atom(s).

The Nature of Two Intense Si–H IR Stretching Bands in FZ‐Si:H

AbstractBased on the isotope effect, two H‐defect complexes: tetrahedral interstitial silane (SiH4)Td and hydrogenated 〈100〉 split interstitials (Isp · 2 H) are proposed to account for the two strong Si–H IR stretching bands in FZ‐Si grown in H atmosphere (2210 cm−1, 1946 cm−1). A series of experimental facts, including the vibration frequency, the correlation with Si–H IR bands in the bending‐wagging region, the temperature dependence of band‐width and the annealing behaviour are presented, which support the proposed model. The results coincide with the view that the self‐interstitial is the dominate thermal defect in crystalline silicon at high temperature.

EPR of neutral vacancy-helium centers in silicon

In this letter we report the first observation by EPR of helium-associated defects in solid. Two new ( S = 1) EPR spectra, labeled Si-AA5 and Si-AA6, arise from the association of helium and intrinsic defects in crystalline silicon. Both are produced by helium ion implantation at room temperature and are stable to 180°C. By implanting 3He isotope, the Si-AA6 3He hyperfine spectrum has been observed. Both centers are tentatively identified as vacancy-helium centers in neutral charge states.

Cluster Computations Related to Silicon Thermal Donors

ABSTRACTAb-initio quantum chemical computations have been applied to a set of molecular clusters derived from Si5 H12 to model defects in crystalline silicon involving boron, carbon, nitrogen, oxygen, and hydrogen. In computations of defect structure, hydrogen atoms terminating silicon valencies are fixed at their computed positions in Si5H12, to represent forces from the lattice, while the position of other atoms are varied.We have computed the stable bonding structures of boron, carbon, nitrogen and oxygen atoms to a vacancy, as well as interstitial oxygen, the silicon-oxygen ylid and two oxygen atoms bound to a vacancy. The structures of the dipositive ions of the oxygen bearing clusters have been computed as part of a search for candidates for the core of the 450° C oxygen thermal donor in silicon crystal. The computed cluster energies are employed to give an account of defect thermochemistry; the addition of the free atoms to a vacancy, the addition of interstitial oxygen atoms to a vacancy, the reaction of interstitial oxygen atoms to form a vacancy-oxygen complex with the emission of silicon monoxide, and the reaction of interstitial oxygen with the dipositive ion of substitutional oxygen to form the dipositive ion of two oxygen atoms bound to a vacancy.

Comparison of impurity defect structures formed by ion implantations in amorphous and crystalline silicon

Impurity defect structures in amorphous and crystalline silicon have been created by the ion implantation of radioactive 119In at room temperature. The defects have been studied by Mössbauer spectroscopy on the 24 keV gamma radiation of the daughter 119Sn. Structurally similar complex defects are concluded to be formed in both phases of the silicon host. The nature of the complex defects depends on the species of implanted impurities. The fraction of complex defects in crystalline silicon increases with increasing implanted dose in the dose range of 10 11 − 10 15 atoms/cm 2. No pronounced discontinuity is observed for the critical dose (⪆ 10 13 atoms/cm 2), where the implanted host volume is amorphised. The implications of these results on the question of a characterisation of the amorphous phase of semiconductors by Mössbauer spectroscopy on implanted impurities will be discussed.

The nature of dangling bonds at line defects in covalent semiconductors

Reports on pseudopotential calculations of the electronic structure at various line defects in crystalline silicon. The authors have determined the density of states and the spatial distribution of charge densities with a view to establishing a link with the existing analogous results for surfaces and point defects (vacancies). In particular, they have focused attention on the localised dangling bond states and have attempted to establish the magnitude of the parameters determining the stability of the line defects considered. They have obtained a consistent picture which is in accord with the intuitive view concerning the short-range nature of the covalent bond.

Light-induced E.S.R. in amorphous silicon

A model for defects in hydrogenated amorphous silicon (TS > 150‡C) observed by light-induced E.S.R. is presented. It is based on a comparison with E.S.R. signals observed from irradiation defects in crystalline silicon. The magnitude of the E.S.R. signal as a function of hydrogen concentration is also discussed.