Th. Wichert

Indium-Defect Complexes in Silicon Studied by Perturbed Angular Correlation Spectroscopy

The formation of molecule-like complexes, consisting of a defect and a radioactive111In atom, is studied using the perturbedγγ angular correlation technique (PAC). The complexes are characterized by their defect specific electric field gradients which also contain information on the geometry of the formed complexes. Whereas the complex is formed with the111In atom, its electric field gradient is measured after the decay of the radioactive111In atom to111Cd. Formation and dissolution of the molecule-like complexes is pursued for a variety of different conditions, such as sample temperature, dopant concentration and position of the Fermi level. In particular, the interaction of In atoms with the following defects in Si was investigated: Intrinsic defects, created by particle irradiation; substitutional donor atoms (P, As, Sb, Bi); and interstitial impurity atoms (Li, H, and an unidentified X defect); especially, the latter ones are known to passivate acceptor atoms in Si. Methodology and specific properties of the PAC technique will be illustrated with the help of these examples.

Doping of the nanocrystalline semiconductor zinc oxide with the donor indium

Doping of the nanocrystalline semiconductor ZnO with the donor 111In was achieved by the incorporation of 111In atoms during the growth process followed by a hydrothermal treatment at 473 K. The incorporation of 111In on substitutional Zn sites was shown by the perturbed γγ angular correlation technique. The structural quality of nanocrystalline ZnO with a mean grain size of 11 nm is significantly improved by annealing at 473 K, as revealed by x-ray diffraction, transmission electron microscopy, optical absorption measurements, and photoluminescence spectroscopy. It is shown that the incorporation of 111In on undisturbed Zn sites in nanocrystalline ZnO seems to be supported by the onset of crystal growth and by the removal of intrinsic defects.

Perturbed angular correlation studies of dopant atom interactions in silicon

The perturbed γγ angular correlation (PAC) technique was used to study the interaction of implanted 111 In probe atoms with the donor atoms P, As, and Sb in Si. Nearest‐neighbor pairs of In‐P, In‐As, and In‐Sb atoms, characterized by νQ1 =179(1), 229(1), and 271(1) MHz, respectively, and having trigonal symmetry about a 〈111〉 axis (η1 =0), were observed after annealing the samples between 540 and 1170 K. These results indicate a strong interaction between acceptor and donor atoms in Si, thus explaining the present and earlier Rutherford backscattering‐channeling results that the In atom solubility in Si was enhanced by the addition of As. The In‐donor atom binding energy was about 0.5 eV. For increasing As concentrations, PAC data showed the appearance of small In‐As atom clusters characterized by νQ2 (As)=238(1) MHz, η2 = 0.65(1); they were probably In‐As2 complexes produced when mobile In atoms were trapped by As2 pairs.

Hyperfine Interactions of Defects in Metals

Hyperfine methods are well established for investigations of solid state properties. There are fields of application, which most recently have developed themselves rather impetously, among them the subject of defects in metals. Information on defects have so far been extracted from macroscopic physical properties like electric resistivity or elastic modulus; in contrast to this the hyperfine methods permit a microscopic glance onto the defect behaviour. Structural and dynamical defect aspects originating from the close vicinity to the radioactive probe atoms as well as the identification of defects on an atomic scale are the main thrust of hyperfine investigations. Originally a handicap for the study of hyperfine interactions following ion implantation or nuclear reactions, the influence of lattice defects became more and more the subject of investigations using hyperfine methods. During the last few years, the method has proved to be a new sensitive tool for defect studies as indicated by the recent proceedings of the international conferences on hyperfine interactions (Uppsala, Sweden, 1974 [4.1]; Leuven, Belgium 1975 [4.2]; Madison, USA, 1977 [4.3]; Berlin, Germany, 1980 [4.4]). Though the defect characteristic hyperfine interaction can be measured by several techniques, the main body of results is obtained by the nuclear techniques like the Mossbauer effect, the perturbed angular correlation and perturbed angular distribution technique.

Perturbed Angular Correlation

Perturbed angular correlation has been established in the past two decades as a powerful tool for the microscopic investigation of solid state properties. It was originally developed and applied to the determination of magnetic dipole and electric quadrupole moments of excited nuclear states, a domain of nuclear physicists. The possibility to get information about internal magnetic fields or electric field gradients, which interact via a hyperfme interaction with the nuclear moments, opened up the field to solid state physics. Today, the precise determination of these electromagnetic fields in the local environment of radioactive probes constitutes the main application of this nuclear method.

Detection of In‐P and In‐Sb atom pairs by perturbed angular correlation in silicon

We report the observation of In‐P and In‐Sb atom pairs in Si using the perturbed γγ angular correlation technique with 111In as radioactive probe atoms. The pairs are characterized by νQ=179(1) MHz and 271(1) MHz, respectively, and their electric field gradient tensors are axially symmetric about a 〈111〉 lattice direction. The results suggest a strong interaction between acceptor and donor atoms in elemental semiconductors like Si and Ge.

Contributions of different defects to the recovery stage at 250 K in gold

Abstract Gold doped with radioactive 111In was irradiated with electrons, protons and Au ions. The trapping of defects at the In atoms during isochronal annealing in stage III was investigated using the perturbed γγ-angular correlation technique (PAC). Via their characteristic electric field gradients four defect configurations were observed. Together with the results of quenched gold specimens we show that the recovery around 250 K is effected by at least two defect types, a small defect cluster being mobile at 195 K and the monovacancy migrating at about 245 K. Additionally, the formation of a large vacancy cluster at the probe impurity is observed at the end of stage III. The occurrence of the different defects is strongly influenced by the mass of the irradiating particles. The results are compared with the information supplied by other experimental methods, especially by resistivity measurements.

Defect configurations in irradiated molybdenum

Abstract Irradiated molybdenum has been investigated by the pertubed angular correlation technique using 111 In as radioactive source. It is observed that defects become trapped at the probe atom in annealing stage III around 500 K. By the quadrupole interaction three different defect configurations are identified; they are characterized by: (1) ν Q = eQV zz / h = 125 MHz, η = ( V yy − V xx )/ V zz = 0, symmetry axis [111]; (2) ν Q = 155 MHz, η = 1 and (3) ν Q = 98 MHz, η = 0, symmetry axis [100]. The defects are assigned to simple defect configurations.

Defects in metals studied by implanted radioactive atoms

Abstract Recent advances in the study of point defects and small defect clusters by nuclear methods are reviewed. Suitable radioactive atoms which fulfill the requirements of the perturbed angular correlation (PAC) or Mossbauer (ME) technique are implanted into solids, where they are used as microscopic probes to investigate their immediate surrounding. Trapping, detrapping or annealing of defects is reflected by changes of the hyperfine interaction between the nuclear moments of the probe atoms and the electromagnetic fields of the defects, while the interaction itself allows the distinct recognition of different defects and can provide detailed information about their structural properties. Experimental data on interstitials, vacancies and clusters in fcc-metals will be quoted as illustrations of the scope of information which can be achieved by hyperfine interaction studies.

Intrinsic limitations of doping diamonds by heavy‐ion implantation

The local environment of 111In implanted into diamonds has been studied by means of the perturbed angular correlation technique as a function of annealing temperature and of implantation dose. It is found that even when the diamond is heated under vacuum to the highest possible temperature before graphitization occurs (2100 K), the implants are not driven to spherically symmetric sites in the lattice. This lack of annealing, if common to all heavy implants, may have serious consequences on the usefulness of doping of diamond by heavy‐ion implantation.