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The perturbed-gamma-gamma-angular-correlation technique (PAC) is a valuable tool for the characterization of defect complexes in crystalline materials. The features of the technique arising in the application to semiconductors are illustrated using the example of In-111-H pairs in Si. This system was studied in the course of an investigation of the passivation of acceptors in Si by H. The consequences of the chemical transmutation of the radioactive probe atoms are discussed. Using Schottky-diode structures, it is shown that PAC is well suited for use in combination with electrical techniques. The PAC technique, which works at any temperature and over a wide range of dopant concentrations, is also sensitive to different charge states of the defect complexes formed. A discussion of the results focuses on the influence of electronic parameters on the electric-field gradient measured at the In-111/Cd-111-H pairs in Si.

The local lattice environment of the donor In in CdS is investigated measuring the electric-field gradient at the site of the radioactive probe atom 111In by the perturbed gammagamma angular correlation technique. It is shown that implantation of In into CdS with subsequent annealing drives 100% of the In atoms to Cd lattice sites. Diffusion of In into CdS under S overpressure results in the formation of InCd-VCd pairs which seem to be responsible for the self-compensation of In donors in CdS (12 References).

The interaction of hydrogen with shallow and deep level impurities in crystalline semiconductors results in a passivation of their electrical activity by the formation of complexes. Nuclear techniques, like the perturbed γγ angular correlation (PAC) and the channeling of charged particles, have contributed to the understanding of the behaviour and microscopic structure of these complexes. A brief introduction to these techniques will be given. The results on the behaviour of hydrogen, in both elemental and compound semi-conductors, will be reviewed. For the case of Si, the information obtained on the formation, geometry and stability of acceptor-hydrogen complexes will be discussed more extensively.

Using the radioactive acceptor 111 In as PAC probe atom, Cd-Cu pairs in Si are observed after the decay of 111 In to 111 Cd. In the temperature range between 100 K up to the dissociation temperature of the pairs (235 K) an increasing dynamic relaxation of the PAC signal is observed. The relaxation rate is reversible within this temperature range. This observation is discussed in the framework of the model of a local diffusion of the Cu atom over the four tetrahedral interstitial sites next to the substitutional Cd atom.

A systematic investigation of the behavior of Cd-implanted GaAs after rapid thermal annealing is presented. The use of various experimental techniques gives a detailed picture regarding the annealing process in the low-dose regime (10(12) and 10(13) cm-2) on a microscopic as well as on a macroscopic scale. Perturbed angular correlation experiments, using the radioactive probe Cd-111m, yield information on the immediate environment of the Cd implant on an atomic scale. Rutherford backscattering channeling and photoluminescence spectroscopy give complementary information concerning the overall damage level in the implanted layer, Hall measurements are used to determine the degree of electrical activation of the implanted Cd acceptors. The outdiffusion of the implanted radioactive Cd atoms is also investigated. The removal of defects in the next-nearest neighborhood of the Cd atoms takes place after annealing at 700 K and is accompanied by a general recovering of the crystal lattice. Between 600 and 900 K more distant defects are removed. The observed outdiffusion of about one-third of the dopant atoms after annealing above 600 K is discussed in context with their partial incorporation in extended defects. Although already at 700 K, 80% of the implanted Cd atoms are on substitutional lattice sites with no defects in their immediate environment, an annealing temperature in excess of 1000 K is necessary to obtain electrical activation of the implants. It is concluded that compensating defects, present in ion-implanted GaAs, are the reason for the significantly higher temperature required for electrical activation as compared to the incorporation of the dopants on defect-free, substitutional lattice sites.

Perturbed Angular Correlation (PAC) and Hall measurements were used to investigate the stability of the passivating Cd-H complex in GaAs after low energy H implantation (150 eV, 1014 cm−2) at 300 K. From the observed Cd-H pair formation and reduction of hole concentration it is deduced that about 10 % of the implanted H atoms form pairs with the Cd atoms. The influence of the dopant depth profile on the apparent stability in zero bias isochronal annealing experiments is reported. After H loading a reduction of carrier mobility is observed, which is stable up to about 400 K. The formation of Cd-H pairs after low energy H implantation into InP was studied by PAC. By measuring the fraction of pairs in an isochronal annealing experiment, the stability of the pairs is deduced yielding a dissociation energy of ED = 1.8 (1) eV.

PAC measurements at 111 In, yielding information on the amount of formed In-H pairs, and four point resistivity measurements were combined to study the correlation between pair formation and electrical deactivation of acceptors in p-Si samples during passivation with H and thermal reactivation. Passivation was performed by means of low energy (200 eV) H + implantation which proved to be quite efficient at 400 K. A complete passivation of the In profile with a peak concentration of 10 18 cm −3 could be achieved. The results show, that the deactivation and reactivation of the In acceptors quantitatively coincide with the formation and dissociation of In-H pairs.

The Cd-H complex in Cd-111m-doped GaAs implanted with low-energy (150-400 eV) hydrogen atoms is identified and studied by perturbed angular correlation spectroscopy using radioactive Cd-111m as a probe. By measuring the fraction of Cd-H pairs in an isochronal annealing experiment, the stability of the pairs is deduced yielding a dissociation energy of E(D) = 1.35(10) eV. After Cd-111m implantation but preceding the H loading, the GaAs samples have to be annealed at temperatures exceeding 900 K in order to form Cd-H pairs. These temperatures are in agreement with the temperature range required for electrical activation of Cd implants, suggesting that a Coulombic interaction is responsible for the formation of Cd-H pairs in GaAs.

Using the perturbed γγ angular correlation technique (PAC) the pairing of Cu with the radioactive acceptor atom 111In in Si is detected. Because of the identity of the electric field gradients the so-called X defect, observed after chemomechanical polishing of Si wafers and known of neutralizing acceptor atoms in Si, is identified as a Cu atom. It is also shown that as-delivered Si wafers already contain Cu atoms which neutralize acceptor atoms if the wafers are annealed at 1173 K.

The presence of Cu atoms in p-type Si is detected via their characteristic electric-field gradients measured at the radioactive acceptor $^{111}\mathrm{In}$${/}^{111}$Cd by the perturbed \ensuremath{\gamma}\ensuremath{\gamma} angular correlation technique. Cu forms pairs with acceptor atoms, thereby electrically passivating them, and is present as a contamination in Si wafers. Using the experimentally known Cu diffusion data and taking into account the effect of ion pairing, a new activation energy of 0.15 eV is deduced, which is in accordance with the dissociation energy of 0.70 eV measured for Coulombic-bound-acceptor\char21{}Cu pairs.

La formation de complexe d'hydrogene accepteur dans Si est etudiee par l'intermediaire des gradients de champ electrique causes par les atomes H dans le site des atomes accepteurs 111 In radioactif

Probing of structural defects in silicon by the perturbed γγ angular correlation (PAC) technique is demonstrated between 77 K and 1300 K. The behaviour of radioactive111 In probe atoms implanted at 295 K, is monitored during isochronal annealing in n-type, p-type and intrinsic Si. Trapping of defects, produced by the111In implantation itself or by postirradiation is studied in P-doped crystals (1016/cm3-1017/cm3).

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.

We have used RBS/Channeling, perturbed angular correlation (PAC) and optical absorption to study the regrowth of disordered layers in diamond produced by implantation with carbon, or with carbon plus boron or indium ions. For C or C plus B implantation doses of 2 ×1015 cm−2 or less, complete recovery of channeling damage occurred after RTA at 1100°C or furnace annealing at 900°C. Optical measurements on samples implanted with high energy carbon ions show better recovery compared to the shallower implantations. PAC results showed that co-implantation with C and In caused a considerable fraction (∼15%) of the In-atoms to occupy well-defined lattice sites characterized by an electric field gradient having its major component along , and a frequency of 116 MHz.

The lattice site of H/D atoms in silicon doped with B and 111In atoms is investigated using the ion channeling and perturbed γγ angular correlation (PAC) technique. The results indicate that at 295 K the antibonding site is occupied by H/D and that this site is easily transformed into a near tetrahedral site under the influence of an analyzing ion beam. Based on PAC results, the population of a second site, possibly a bond-center site, is expected at low temperatures.

The interaction of acceptor atoms with the interstitial impurity atoms hydrogen and lithium in the semiconductors silicon and germanium has been studied with help of the perturbed γγ angular correlation technique at the radioactive acceptor 111 In. The formed acceptor-donor pairs, as characterized by their electric field gradients, show some striking differences in silicon and germanium. In particular, besides the thermal stability of the pairs, the number of formed InLi and InH complexes is different in silicon and germanium. The behaviour of the formed complexes as a function of the carrier concentration will be discussed.