Resonant and localised modes due to boron in gallium arsenide

Silicon-doped n-type GaAs crystals pulled from a melt encapsulated with boric oxide exhibit an IR absorption band at 123 cm^?1 as well as a number of localised-mode bands associated with boron and silicon. Evidence is presented which leads us to attribute the band at 123 cm^?1 to a resonant mode associated with isolated B atoms on Ga sites. Other crystals containing high concentrations of silicon or phosphorous did not show such an absorption band. The results are discussed briefly in terms of the simple mass defect model for impurity vibrations.     

Ionization mechanisms of aluminum acceptor impurity in silicon

Processes of ionization of shallow acceptor centers (ACs) in silicon are studied. In crystalline silicon samples with phosphorus (1.6×10¹³, 2.7×10¹³, and 2.3×10¹⁵cm^?3) and boron (1.3×10¹⁵cm^?3) impurities, _μAl impurity atoms were produced by implantation of negative muons. It is found that thermal ionization is the main mechanism for ionizing the Al acceptor impurity in both p-type and n-type silicon with an impurity concentration of ?10¹⁵cm^?3 at T>45 K. The thermal ionization rate of Al ACs in Si varies from ～10⁵ to ～10⁶s^?1 in the temperature range 45–55 K.     

Influence of irradiation on the thermal decomposition of lithium perchlorate

Abstract

Infrared absorption measurements were made before and after 90 °K electron irradiations of silicon samples which contained either dispersed oxygen, carbon, or carbon plus oxygen. Irradiation-produced absorption bands associated with two distinctly different defects are observed depending on the oxygen and carbon content of the silicon. One center is the well-known vacancy-oxygen A-center defect (836-cm^?1 band) and is formed on irradiation in oxygen-containing silicon with a magnitude which is independent of the carbon content. Measurements have correlated the formation of one A-center with the loss of one interstitial oxygen atom, thereby indicating that A-center formation occurs by vacancy trapping at interstitial oxygen atoms. A second center (922-and 932-cm^?1 bands) is formed only in silicon crystals which contain both oxygen and carbon. The results indicate that this center is formed by the trapping of a silicon interstitial at a carbon-oxygen complex.     

Superior tolerance of Ag/Ni multilayers against Kr ion irradiation: an in situ study

Monolithic Ag and Ni films and Ag/Ni multilayers with individual layer thickness of 5 and 50?nm were subjected to in situ Kr ion irradiation at room temperature to 1 displacement-per-atom (a fluence of 2?×?10¹⁴?ions/cm²). Monolithic Ag has high density of small loops (4?nm in diameter), whereas Ni has fewer but much greater loops (exceeding 20?nm). In comparison, dislocation loops, ～4?nm in diameter, were the major defects in the irradiated Ag/Ni 50?nm film, while the loops were barely observed in the Ag/Ni 5?nm film. At 0.2?dpa (0.4?×?10¹⁴?ions/cm), defect density in both monolithic Ag and Ni saturated at 1.6 and 0.2?×?10²³/m³, compared with 0.8?×?10²³/m³ in Ag/Ni 50?nm multilayer at a saturation fluence of ～1?dpa (2?×?10¹⁴?ions/cm²). Direct observations of frequent loop absorption by layer interfaces suggest that these interfaces are efficient defect sinks. Ag/Ni 5?nm multilayer showed a superior morphological stability against radiation compared to Ag/Ni 50?nm film.     

Optical and electrical properties of GaN: Si-based microstructures with a wide range of doping levels

The optical and electrical properties of silicon-doped epitaxial gallium nitride layers grown on sapphire have been studied. The studies have been performed over a wide range of silicon concentrations on each side of the Mott transition. The critical concentrations of Si atoms corresponding to the formation of an impurity band in gallium nitride (～2.5 × 10¹⁸ cm^?3) and to the overlap of the impurity band with the conduction band (～2 × 10¹⁹ cm^?3) have been refined. The maximum of the photoluminescence spectrum shifts nonmonotonically with increasing doping level. This shift is determined by two factors: (1) an increase in the exchange interaction leading to a decrease in the energy gap width and (2) a change in the radiation mechanism as the donor concentration increases. The temperature dependence of the exciton luminescence with participating optical phonons has been studied. The energies of phonon-plasmon modes in GaN: Si layers with different silicon concentrations have been measured using Raman spectroscopy.     

Effect of the doping level on temperature bistability in a silicon wafer

The influence of the doping level on the effect of the temperature bistability in a silicon wafer upon radiative heat transfer between the wafer and the elements of the heating system is studied. Theoretical transfer characteristics are constructed for a silicon wafer doped with donor and acceptor impurities. These characteristics are compared with the transfer characteristics obtained during heating and cooling of wafers with the hole conduction (with dopant concentrations of 10¹⁵, 2 × 10¹⁶, and 3 × 10¹⁷ cm^?3) and electron conduction (with impurity concentrations of 10¹⁵ and 8 × 10¹⁸ cm^?3) in a thermal reactor of the rapid thermal annealing setup. It is found that the width and height of the hysteresis loop decrease with increasing dopant concentration and are almost independent of the type of conduction of the silicon wafer. The critical value of the impurity concentration of both types is 1.4 × 10¹⁷ cm^?3. For this concentration, the loop width vanishes, and the height corresponds to the minimal value of the temperature jump (～200 K). The mechanism of temperature bistability in the silicon wafer upon radiative heat transfer is discussed.     

Dislocation-induced photoluminescence in silicon crystals of various impurity composition

The effect of oxygen on the dislocation-induced photoluminescence (DPL) spectra at 4.2 K is studied in silicon crystals with different impurity compositions subjected to plastic deformation at temperatures above 1000°C. A strong effect of doping impurities on the DPL spectra is observed for concentrations above 10¹⁶ cm^?3. It is shown that the peculiarities of many DPL spectra in silicon can be explained by assuming that the D1 and D2 lines are associated with edge-type dislocation steps on glide dislocations.     

Irradiation damage in carbon-doped silicon irradiated at low temperatures by 2 MeV electrons

Abstract

Irradiation of silicon by 2 MeV electrons at 130°K leads to the removal of carbon from substitutional sites and the formation of centres with axial symmetry having vibrational modes at 921 and 930 cm^?1 for ¹²C; large isotope shifts are found in crystals containing ¹³C and ¹⁴C. This centre is considered to involve interstitial carbon atoms but not oxygen impurities. On annealing such irradiated crystals to room temperature the concentration of these centres is reduced and a new transient centre involving carbon has been detected. Further annealing leads to the formation of the well known 11.56μm absorption band in pulled crystals and it is shown that this may be correlated with another band at 1115.5 cm^?1. Again large isotope effects are found in crystals containing ¹³C and ¹⁴C and this centre is ascribed to a [O-C] complex involving an interstitial carbon atom.     

Magnetic moment relaxation of a shallow acceptor center in heavily doped silicon

Results of studying the temperature dependence of the residual polarization of negative muons in crystalline silicon with germanium (9×10 ¹⁹ cm ^?3 ) and boron (4.1×10 ¹⁸ , 1.34×10 ¹⁹ , and 4.9×10 ¹⁹ cm ^?3 ) impurities are presented. It is found that, similarly to n-and p-type silicon samples with impurity concentrations up to ～10 ¹⁷ cm ^?3 , the relaxation rate ν of the magnetic moment of a _μ Al acceptor in silicon with a high impurity concentration of germanium (9×10 ¹⁹ cm ^?3 ) depends on temperature as ν～T ^q , q≈3 at T=(5–30) K. An increase in the absolute value of the relaxation rate and a weakening of its temperature dependence are observed in samples of degenerate silicon in the given temperature range. Based on the experimental data obtained, the conclusion is made that the spin-exchange scattering of free charge carriers makes a significant contribution to the magnetic moment relaxation of a shallow acceptor center in degenerate silicon at T?30 K. Estimates are obtained for the effective cross section of the spin-exchange scattering of holes (σ _h ) and electrons (σ _e ) from an Al acceptor center in Si: σ _h ～10^?13 cm² and σ _e ～8×10^?15 cm² at the acceptor (donor) impurity concentration n _a (n _d )～4×10¹⁸ cm^?3.     

Kinetics of accumulation of vacancy complexes in dislocated silicon under 60Co γ-ray irradiation

Abstract

Radiation defect accumulation in ⁶⁰Co γ-ray-irradiated n-type Si single crystals (ρ=150ωcm) with various densities of dislocations (N_D = 1 × 10⁴ to 1 × 10⁷ cm ^?2) introduced at plastic deformation was studied. The temperature dependences of the Hall coefficient were measured. The probabilities of interaction of vacancies with oxygen, phosphorus atoms, and dislocation line elements were determined. It has been established that with the increase of N_D they can increase at the expense of complication of dislocation structure, decrease during formation of impurity atmosphere near dislocations and compensation of deformation fields, and they do not change if complex formation of vacancies with impurities occurs far from dislocations. Kinetics of A- and E-centre accumulation in the crystals containing dislocations with different impurity atmosphere was described.     

Accelerated oxygen precipitation in fast neutron irradiated Czochralski silicon

Annealing effect of the oxygen precipitation and the induced defects have been investigated on the fast neutron irradiated Czochralski silicon （CZ-Si） by infrared absorption spectrum and the optical microscopy. It is found that the fast neutron irradiation greatly accelerates the oxygen precipitation that leads to a sharp decrease of the interstitial oxygen with the annealing time. At room temperature （RT）, the 1107cm^-1 infrared absorption band of interstitial oxygen becomes weak and broadens to low energy side. At low temperature, the infrared absorption peaks appear at 1078cm^-1, 1096cm^-1, and 1182cm^-1, related to different shapes of the oxygen precipitates. The bulk microdefects, including stacking faults, dislocations and dislocation loops, were observed by the optical microscopy. New or large stacking faults grow up when the silicon self-interstitial atoms are created and aggregate with oxygen precipitation.     

Effect of correlation in the impurity defect distribution on the micromechanical properties of GaAs: Te single crystals

The micromechanical properties of Te-doped GaAs single crystals with free carrier density n ₀ = 10¹⁷?5 × 10¹⁸ cm^?3 were studied. The obtained data are as follows: the nonmonotonic concentration dependences of the microhardness, the lengths of dislocation rosette rays, the densities of dislocations, and the position and half-width of the Raman line of a transverse optical phonon. The data are interpreted in terms of spatial correlation in the impurity defect distribution.     

The X-ray diffraction intensity of cyclically loaded Al

The displacement field around a dislocation loop had been calculated to give the diminishing factor of X-ray diffraction intensity from a fatigued Al sample. Experimentally had been measured this factor on the samples fatigued at room temperature and at low temperature. From these the size and density of dislocation loops can be deduced. Results show that in the sample fatigued at room temperature there is no significant change in dislocation structure while at low temperature in fatigued sample occurs a large amount of dislocation loops whose density is 10¹⁴?10¹⁷cm^?3 while their radii are between 100 and 1000 Å.     

Dynamic properties of dislocations in silicon wafers heat-treated at low temperatures

The specific features of the dislocation motion in dislocation-free silicon wafers (single crystals are grown by the Czochralski method) heat-treated at 450 and 650°C have been investigated. It is found that the low-temperature treatment of silicon wafers with an oxygen content of (7–8)×10¹⁷ cm^?3 substantially affects the dynamic properties of dislocations generated into silicon wafers during their four-point bending and brings about an increase in the starting stresses of the onset of the dislocation motion. A characteristic spatial inhomogeneity is observed in the generation and propagation of dislocations from indentations upon the bending of heat-treated wafers. The reasons for the regularities revealed are discussed.     

The effect of uniaxial static pressure on the behavior of an aluminum acceptor impurity in silicon

The effect of uniaxial compression on the behavior of shallow aluminum acceptor centers in silicon has been studied. The _μAl impurity atoms were created by implanting negative muons into silicon single crystals doped with phosphorus to 1.6×10¹³ cm^?3 (sample 1) and 1.9×10¹³ cm^?3 (sample 2). The muon polarization was studied in the temperature range 10–300 K. Measurements were performed in a magnetic field of 2.5 kG oriented perpendicularly to the muon spin. The samples were oriented so that the selected crystal axis ([111] and [100] in samples 1 and 2, respectively), the magnetic field, and the initial muon-spin polarization were mutually perpendicular. External pressure applied to the sample along the indicated crystal axis changed both the absolute value of the acceptor magnetic-moment relaxation rate and the character of its temperature dependence.     

Optical spectra of (CdF2)0.9(InF3)0.1 semiconductor solid solutions

The differences in the optical spectra of CdF₂:In semiconductors with bistable DX centers (concentrated (CdF₂)_0.9(InF₃)_0.1 solid solutions) and “standard” samples with a lower impurity concentration used to record holograms are discussed. In contrast to the standard samples, in which complete decay of two-electron DX states and transfer of electrons to shallow donor levels may occur at low temperatures, long-term irradiation of a (CdF₂)_0.9(InF₃)_0.1 solid solution by UV or visible light leads to decay of no more than 20% deep centers. The experimental data and estimates of the statistical distribution of electrons over energy levels in this crystal give the total electron concentration, neutral donor concentration, and concentration of deep two-electron centers to be ～5 × 10¹⁸ cm^?3, ～9 × 10¹⁷ cm^?3, and more than 1 × 10²⁰ cm^?3, respectively. These estimates show that the majority of impurity ions are located in clusters and can form only deep two-electron states in CdF₂ crystals with a high indium content. In this case, In³⁺ ions in a limited concentration (In³⁺ (～9 × 10¹⁷ cm^?3) are statistically distributed in the “unperturbed” CdF₂ lattice and, as in low-concentrated samples, form DX centers, which possess both shallow hydrogen-like and deep two-electron states.     

Ionic conductivity of lithium nitride doped with hydrogen

Lithium ionic conductivity of Li₃N single crystals is reported for temperatures from 120 K to 350 K. The intrinsic ionic conductivity is rather small (< 10^?6 Ω^?1 cm^?1 at 300 K) and shows no strong anisotropy. The activation energy is near 0,6 eV. It is shown that hydrogen is the critical impurity in the crystals grown and studied at this laboratory. The relative impurity concentration is determined from infrared transmission measurements near 3130 cm^?1. An estimate for absolute values is obtained from dielectric studies. Increases in ionic conductivity with hydrogen doping by a factor 5000 are reported for E⊥c but no significant effects are found for E6c. The proposed defect is an impurity-vacancy complex consisting of an NH^?? and a lithium vacancy.     

In situ study of self-ion irradiation damage in W and W–5Re at 500 °C

In situ self-ion irradiations (150?keV?W⁺) have been carried out on W and W–5Re at 500?°C, with doses ranging from 10¹⁶ to 10¹⁸ W⁺m^?2 (～1.0?dpa). Early damage formation (10¹⁶W⁺m^?2) was observed in both materials. Black–white contrast experiments and image simulations using the TEMACI software suggested that vacancy loops were formed within individual cascades, and thus, the loop nucleation mechanism is likely to be ‘cascade collapse’. Dynamic observations showed the nucleation and growth of interstitial loops at higher doses, and that elastic loop interactions may involve changes in loop Burgers vector. Elastic interactions may also promote loop reactions such as absorption or coalescence or loop string formation. Loops in both W and W–5Re remained stable after annealing at 500?°C. One-dimensional hopping of loops (b?=?1/2 ?111>) was only seen in W. At the final dose (10¹⁸W⁺m^?2), a slightly denser damage microstructure was seen in W–5Re. Both materials had about 3–4?×?10¹⁵ loops m^?2. Detailed post-irradiation analyses were carried out for loops of size???4?nm. Both b?=?1/2 ?111? (～75%) and b?= ?100> (～25%) loops were present. Inside–outside contrast experiments were performed under safe orientations to determine the nature of loops. The interstitial-to-vacancy loop ratio turned out close to unity for 1/2 ?111? loops in W, and for both 1/2 ?111? and ?100? loops in W–5Re. However, interstitial loops were dominant for ?100? loops in W. Re seemed to restrict loop mobility, leading to a smaller average loop size and a higher number density in the W-Re alloy.     

High pressure raman study of Bi-2212

The hydrostatic pressure dependence of the Raman spectra of Bi₂Sr₂CaCu₂O₈ single crystals has been investigated. The energy of the A _g and B _1g modes was found to increase with pressure in agreement with previously reported measurements, except the strong mode at ～465 cm^?1, which softens with pressure, while another peak at ～458 cm^?1 appears more pronounced at low temperatures and high pressures. The energy of both modes does not seem to change with increasing pressure, up to ～5 GPa, although the average energy of the wide band has been found to soften, which is in disagreement with previously published results. Based on the modifications observed in some phonons at ～1.8 GPa, which correlate with the reduction of T _c and the deformations of the CuO₅ pyramids, we attribute the mode at ～465 cm^?1 to the vibrations of the apex oxygen atoms. All modes due to the oxygen atoms were found to be strongly anharmonic.     

Impurity redistribution in Pb implanted and annealed silicon

Reordering of 〈111〉 silicon, implanted with Pb ions at energies >100 keV and fluences ～5 × 10¹⁵ cm^?2 is accompanied by substantial impurity indiffusion in addition to pronounced outdiffusion and accumulation at the near surface region.