Multivacancy Complexes Research Articles

DLTS spectra of silicon diodes with p+-n-junction irradiated with high energy krypton ions

p+-n-Diodes have been studied. The diodes were manufactured on wafers (thickness 460μm, (111) plane) of uniformly phosphorus doped float-zone-grown single-crystal silicon. The resistivity of silicon was 90Ωcm and the phosphorus concentration was 5×1013cm−3. The diodes were irradiated with 250MeV krypton ions. The irradiation fluence was 108cm−2. Deep-level transient spectroscopy (DLTS) was used to examine the defects induced by high energy krypton ion implantation. The DLTS spectra were recorded at a frequency of 1MHz in the 78–290K temperature range. The capacity-voltage characteristics have been measured at a reverse bias voltage from 0 to −19 V at a frequency of 1MHz. We show that the main irradiation-induced defects are A-centers and divacancies. The behavior of DLTS spectra in the 150–260K temperature range depends essentially on the emission voltage Ue. The variation of Ue allows us to separate the contributions of different defects into the DLTS spectrum in the 150–260K temperature range. We show that, in addition to A-centers and divacancies, irradiation produces multivacancy complexes with the energy level Et = Ec−(0.5±0.02) eV and an electron capture cross section of ~4×10–13cm2.

DLTS SPECTRA OF SILICON DIODES WITH P+—N–JUNCTION IRRADIATED WITH HIGH ENERGY KRYPTON IONS

p +- n -Diodes have been studied. The diodes were manufactured on wafers (thickness 460 μm, (111) plane) of uniformly phosphorus doped float–zone–grown single–crystal silicon. The resistivity of silicon was 90 Ohm · cm and the phosphorus concentration was 5 · 1013 cm–3. The diodes were irradiated with 250 MeV krypton ions. The irradiation fluence was 108 cm–2. Deep–level transient spectroscopy (DLTS) was used to examine the defects induced by high energy krypton ion implantation. The DLTS spectra were recorded at a frequency of 1 MHz in the 78—290 K temperature range. The capacity–voltage characteristics have been measured at a reverse bias voltage from 0 to –19 V at a frequency of 1 MHz. We show that the main irradiation–induced defects are A–centers and divacancies. The behavior of DLTS spectra in the 150—260 K temperature range depends essentially on the emission voltage U e. The variation of U e allows us to separate the contributions of different defects into the DLTS spectrum in the 150—260 K temperature range. We show that, in addition to A–centers and divacancies, irradiation produces multivacancy complexes with the energy level E t = E c – (0.5 ± 0.02) eV and an electron capture cross section of ~4 · 10–13 cm2.

Interlayer vacancy diffusion and coalescence in graphite

Due to the layered nature of graphite, the migration and interaction of point defects in the graphite crystal structure are highly anisotropic, and it is usually assumed that individual mobile lattice vacancies are confined to diffuse on a single plane. We present the results of ab initio calculations based on density functional theory which demonstrate that vacancies can, in fact, move between adjacent planes when they interact with one another via relatively low energy pathways, often with barriers of less than 1 eV. These interlayer transition mechanisms can significantly alter both the kinetics of point-defect aggregation and coalescence and also the resultant morphologies of multivacancy complexes that form as a result of migrating vacancies interacting.

Radiation Damage Effects on Optical, Electrical, and Thermophysical Properties of CVD Diamond Films

Raman and IR spectroscopy and thermal conductivity were employed to investigate the effects of simultaneous vacuum annealing on defect transformation processes in diamonds irradiated by fast neutrons and nanocrystalline diamond films (DF) implanted with O or P ions. A correlation between the thermal conductivity at room temperature and the absorption coefficient near 13 μm was found in diamonds irradiated by neutron fluence 2⋅1019 cm–2. It was found that two-phonon absorption in diamond IR spectra was sensitive to destruction of long-range ordering in the diamond crystal lattice. An absorption band with a shape characteristic of localized centers in the band gap (activation energy ~0.25 eV) was identifi ed in IR spectra of DF irradiated by neutrons and annealed at temperatures <900°C. It was shown that the optical and transport properties of the studied radiation-damaged DF were determined by multi-vacancy complexes and inclusions of a non-diamond phase.

μ-Raman Spectra Analysis of the Evolution of Hydrogen Related Defects and Void Formation in the Silicon Ion-Cut Process

AbstractHydrogen implanted, boron doped (100) Czochralski silicon wafers, which were annealed after implantation up to 600 °C, are investigated by μ-Raman spectroscopy (μRS). We have studied the thermal evolution of hydrogen related defects, including vacancy-hydrogen (VnHm) complexes, H-saturated dangling bonds and trapped H2 molecules. Applying temperatures above ∼ 400 °C, the hydrogen related defects and the formation of voids/platelets are distinctly modified. The measured intensity of the local vibration mode (LVM) of H2 molecules trapped in multi-vacancy complexes at a frequency of ∼ 3820 cm-1 decreases while the LVM of H2 in platelets or larger voids (∼ 4150 cm-1) is increasing. This indicates that multi-vacancy complexes coalesce and form larger voids/platelets. Most of the VnHm complexes (∼ 2000 – 2200 cm-1) are dissolved during annealing at 600 °C, where a thin silicon layer exfoliates due to the ion-cut mechanism. However, the Raman modes of the characteristic V2H6 complex, of Si-Hx bonds stemming from H-terminated surfaces and of H2 located in voids/platelets still can be observed after a short time annealing (≤2 min) at 600 °C.

The fluence effect in hydrogen-ion cleaving of silicon at the sub-100-nm scale

The implementation at the sub-100-nm scale of ion cleaving requires ion beams of ∼5 keV/amu or less. The blistering efficiency in 5-keV H-ion-implanted and annealed Si has been found to peak and vanish in a narrow range of ion fluence of (1.5–3.5)×1016 H/cm2. In order to understand this effect, the defect profiles in 5-keV H-irradiated Si were studied by Rutherford backscattering/channelling, while the Si-H bonding configurations during annealing were investigated by Raman scattering spectroscopy. Three types of defects play major roles: the ‘broad-band’ monohydride multivacancy complexes, the fully or partially passivated monovacancy VHn, and H-terminated internal surfaces Si(100):H. Blister absence at high fluence is characterised by the persistence up to 550 °C of the Si(100):H structures, which are blister embryos that failed to coalesce and grow. Radiation-induced stresses and fracture toughening may play roles in inhibiting cleavage at high fluence; however, widening towards the surface of the zone of high H and defect concentration is the likely major factor.

Vacancy clusters in diamond studied by electron spin resonance

We report on the electron spin resonance characterization of dominant paramagnetic defects created in pure diamond by neutron irradiation followed by annealing at temperatures above 1150 °C. Along with the previously reported R7, R8, R10a, and R12 centers, two extra S = 1 centers, labeled as R7a and KUL13, and two S = 1/2 centers KUL14 and KUL15 have been detected and characterized. From the angular variation of the ESR line positions, the symmetry of the R7, R7a, KUL13, KUL14 and KUL15 centers was inferred as monoclinic-I, C2v, C3v, monoclinic-I and almost C2v, respectively. The analysis of the D matrix properties suggests that the R7, R7a, and R8 centers originate from multivacancy complexes, where unpaired electrons are separated by three vacancy sites. Those centers were tentatively associated with closed structures of eleven, nine and thirteen vacancies, respectively. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Cathodoluminescence of cubic boron nitride films deposited by chemical vapor deposition

Cathodoluminescence (CL) characteristics of cubic boron nitride (cBN) films deposited by chemical vapor deposition were investigated. Combined with the results from Fourier-transformed infrared spectroscopy and Raman spectroscopy, the dependence of the emission energy and intensity on the phase composition and crystallinity of the films was revealed. A broad emission band centered at about 3.12 eV for UCL (or US-1) as observed previously in undoped cBN single crystals synthesized by high-temperature, high-pressure method, and an emission band at about 2.48 eV for the A and B bands, due to multivacancy complexes of boron and nitrogen vacancies, were observed in the cBN films with high phase purity and high crystallinity. For the hexagonal boron nitride (hBN) phase, the main emission band up-shifted to high energy of 3.48–3.68 eV. A peak centered at 5.28 eV was observed in the spectra, which is believed the near-band-gap UV emission of hBN.

Electron paramagnetic resonance study of proton implantation induced defects in monocrystalline 4H– and 6H–SiC

Ion implantation is frequently employed in SiC for doping, electrical isolation or in the SiC on isolator technology. The ion implantation process is accompanied by the formation of intrinsic defects, which introduce deep electron and hole traps. They are believed to be mainly multivacancy complexes but the exact microscopic nature of these defects and their distribution versus the ion penetration depth is not well established. We have analyzed by electron paramagnetic resonance spectroscopy the defects introduced by high energy (MeV) proton implantation. In this study we extend the previous investigations on n-type SiC to the case of p-type Al doped bulk samples. Both silicon monovacancy and carbon vacancy related defects are observed. Their nature and introduction rate have been determined. The results obtained will be compared to the published electrical studies in order to correlate the vacancy defects with the known electron and hole traps.

Study of indium-defect interactions in diamond using two-dimensional conversion-electron emission channelling

Channelling has, since its inception, proven to be a valuable tool in locating the geometric position of atoms in the crystal lattice. Allied with powerful theoretical models, it can yield detailed information on the positions that these impurities occupy. 111In, a radioactive isotope with a conveniently short half-life, is an often-used probe of heavy-atom doping of materials. Previous work has centred on the lattice location of 111In implanted in type IIa diamond. Theoretical calculations on this `pure' system have also recently been made. We have performed the first studies of 111In implanted into various carefully selected, defect-rich diamond systems and obtained fractions for the sites occupied. The defect systems investigated include nitrogen in various configurations, boron, hydrogen and vacancies. The use of two-dimensional conversion-electron emission channelling (CEEC) has enabled the system to be studied in greater detail than with conventional one-dimensional CEEC. Coupled with the acquisition of the CEEC spectra for all the major channelling axes, this has yielded a comprehensive data set. The spectra are consistent with a pure substitutional fraction as well as another fraction, approximately 0.45 Åfrom the substitutional along a 111 direction. Previous measurements observed these two components together as substitutional or `near-substitutional'. The data have been compared to simulated CEEC spectra and earlier quantum chemical calculations. The pure substitutional fraction is indicated to be in a defect-free configuration while the component displaced away from substitutional involves most probably the divacancy and another nearby defect. The results show no dependence on impurity type, even after annealing. If indium complexation with these defects does occur it is shown not to measurably affect the channelled spectra and thus the projected lattice location of the 111In probe. The origin of the random fraction measured in previous studies is proposed to be partially due to In in different multi-vacancy complexes. Taken together, the data indicate the importance of vacancies (complexes) in the final configuration for In after implantation in diamond.

Radiation defects and electrical properties of silicon layers containing Sb and As implanted with Si + ions

Accumulation and annealing of the radiation defects in silicon layers containing Sb and As and implanted with Si + ions have been investigated with the help of EPR and X-ray diffraction methods. For n-type silicon with high doping level the dose of the beginning of amorphization is decreased in comparison with that for low doped samples. This effect is explained by the appearance of the Coulomb barrier for the annihilation of charged defects having the same electrical charge sign. Impurities of Sb and As have been established to be the part of the multivacancy complexes with an increased thermal stability by 100°C in comparison with intrinsic complexes in silicon.

Theory of te precipitation and related effects in CdTe Crystals

A thermodynamic calculation is presented which explains the origin of often reported large stress fields in and around Te precipitates and associated punching of dislocation loops in star like patterns. The calculation is based on the consideration that the stoichiometric deviation in Te saturated crystals are accommodated by Te interstitials, Cd multivacancy complexes and Te antisites; the Te interstitials are most mobile of them, and dominate the precipitation process; and the precipitates when they appear first are in droplet form. The droplet state is modelled on the basis of the Lennard-Jones 6-12 interaction potential. The droplet growth is envisaged to occur via the following two processes operating in tandem: first, capture of excess Te interstitials to cause droplet overpressurization, and then, punching of interstitial dislocation loops whenever the pressure exceeds a threshold value. The flow of Te interstitials into the droplets is driven by the difference between their formation energies in the lattice and the free energy change of the droplets per Te atom added. It is shown that the achievable droplet pressures far exceed that required for the loop punching and sustaining the growth cycle. The occurrence of varying precipitate morphologies are explained, and the possibility of nucleating high presssure Te phases is examined. Some experimental evidence is also presented which corroborate the theoretical arguments involved.

Perturbed γ−γ angular correlations: A spectroscopy for point defects in metals and alloys

Atomic defects which migrate and trap at impurity probe atoms can be labelled by the changes they induce in the hyperfine interactions of the probe nuclei. Many studies have been made using perturbed γ−γ angular correlations (PAC) and the111In probe because of the excellent resolution of different sites. Identification of the bound states is the key problem in applying hyperfine interactions methods to point defects studies. In this study three structure-sensitive methods are applied to help identify the atomic structures of various multivacancy complexes in Pt and Au: (1) Quadrupole interaction parameters are compared with results of point-charge calculations of electric-field gradients for 20 structures containing 1–4 vacancies in the fcc lattice. (2) Hyperfine interactions induced by decorating vacancy complexes with hydrogen atoms are measured and interpreted with the assistance of point-charge calculations. (3) Transformations between complexes observed by annihilation of vacancies by mobile self-interstitials are used to test the consistency of the identifications. Using these methods in conjunction with analysis of the trapping behavior which occurs during annealing of damaged samples, structural models are presented for divacancy (2V), 3V and 4V complexes in Pt, and 3V and 4V complexes in Au. The activation temperatures of the 3V defect in Au and Pt are determined to be 162 K and 390 K, respectively, and activation temperatures of defects in Ni, Cu, Pt and Au are compared. For Pt, trapping of H at 1V and 2V complexes is observed to lead to small changes in the quadrupole interactions, consistent with well shielded protonic charges. However, trapping at 3V and 4V complexes leads to very large changes which we attribute to atomic restructuring to the defect complexes. Finally, the application of the same methodology to interpret recent experiments on NiAl, an ordered alloy, is described.

Investigation of neutron radiation defects in silicon by high discriminability deep level transient spectroscopy (HDDLTS)

Neutron radiation induced defects in neutron-transmutation doped (NTD) silicon containing preexisting electron traps have been investigated by means of high discriminability deep level transient spectroscopy (HDDLTS). The experimental results show that the preexisting defects influence the formation and annealing behavior of neutron radiation-induced defects, and reduce the introduction rates of some radiation defects. Some of the radiation defects and the preexisting defects are suggested to be di- or multi-vacancy complexes.

Kinetics of vacancy-impurity complexes in fcc-cobalt

The perturbed angular correlation method was used to study the defect kinetics after111In implantation into epitaxial fcc-Co layers. The combined magnetic and electric hyperfine interaction of the different complexes enabled us to follow the migration of vacancies and multi-vacancy complexes, via their trapping and release at the In probe atoms. The nucleation of multi-vacancy complexes is discussed in some detail.

Interaction of radiation defects with the surface of silicon

The formation and annealing processes of radiation defects in bulk crystals and thin (≈︁ 1.2 μm) epitaxial layers of Si are studied. Czochralski grown (pulled) and vacuum float-zone n-type Si crystals with ϱ = 1 to 2 Ωcm as well as n-type Si epitaxial layers (∂ ≈︁ 1 Ωcm) grown on substrates of p-type Si, 400 pm thick (ϱ ≈︁ 10 Ωcm) are used. The samples are irradiated (T ⪷ 50 °C) by 640 MeV protons. Results are obtained from the analysis of the temperature dependences of the Hall coefficient at various steps of irradiation or 15 min isochronous annealing as well as from the spatial distributions (over the layer thickness) of the doping impurity and irradiation- and annealing-produced defect concentration. It is established that due to the interaction with the surface of irradiation-generated vacancies and interstitials as well as mobile defects and their components migrating at annealing, a number of peculiarities in radiation defect accumulating and annealing processes take place in epitaxial layers of Si as compared to bulk crystals: 1) Lower charge-carrier removal rates due to the low E-centre introduction efficiency whereby they are not the main compensating defects in thin layers whose thickness is comparable to the vacancy diffusion length; 2) sufficiently wide radiation defect annealing range; 3) effective production of multivacancy complexes under heat treatment near the surface. The results obtained are explained taking into account electric fields and long-range elastic stress fields near the surface. [Russian Text Ignored].

Study of Rearrangements of Intrinsic Defects at Annealing of Proton‐Irradiated Silicon

AbstractRearrangement processes proceeding during annealing of electrically active radiation defects in heavily irradiated (30 MeV protons) Si when the concentration of primary defects induced exceeds the concentration of impurities available in crystal are studied. Czochralski grown and vacuum floating‐zone n‐ and p‐type silicon (ϱ = 3 to 500 Ω cm) are used. Experimental results obtained from the analysis of the Hall coefficient temperature dependences show that the rearrangement of intrinsic structural defects (diinterstitials and multivacancy complexes) occurs predominantly during annealing. Accumulation kinetics is studied and temperature stability range of some multivacancy complexes contributing to the forbidden gap energy levels Ev + 0.29 eV (400 to 650 °C), Ev + 0.32 eV (500 to 750 °C), Ev + 0.22 eV (500 to 700 °C), Ev + 0.15 eV (500 to 800 °C), Ev + + 0.10 eV (600 to 750 °C), Ec −0.24 eV (500 to 850 °C) most of which are acceptor levels is determined. The diinterstitial (Si‐B3) center being annealed in the temperature range 300 to 500 °C is supposed to be a multicharge defect and has deep acceptor ( Ec −0.40 eV) and donor ( Ev + 0.35 eV) levels.