Optical detection of magnetic resonance (ODMR) is reported for ZnSe irradiated by 2.5 MeV electrons in situ at 4.2K. Interstitial zinc atoms are detected in both isolated form and paired with zinc vacancies (Frenkel pairs) of many resolved discrete separations. The isolated interstitial produces a deep second donor state (+/++) at ∼Ec -0.8 eV and its activation energy for migration is estimated to be ∼0.6–0.7 eV. The Frenkel pairs give rise to efficient localized donor-acceptor recombination luminescence and the exchange interactions between the electron and hole on the two partners are measured directly by ODMR.

A simple way to extend the remarkable results of Density Functional calculations to finite-temperature properties of materials is the quasi-harmonic theory of Lattice Dynamics. In this framework a thermodynamically consistent theory needs the complete phonon spectrum for a large periodic system (30–100 atoms/cell) at many different volumes, which poses severe practical limitations. In this paper I present the application to a semiconducting system of a method recently proposed by Bachelet and De Lorenzi to overcome these limitations. Based on low-temperature Molecular-Dynamics trajectories (now possible from first principles for semiconducting systems according to the method of Car and Parrinello), the method is shown to provide accurate dynamical matrices for an 8-atom silicon supercell. Such a successful, preliminary test, together with the fact that for larger and/or lower-symmetry systems the computational effort required by the “trajectory approach” is lower than traditional frozen-phonon or force-constant techniques, suggests its use in the determination of dynamical matrices of larger defect or amorphous systems, and thus in the study of their thermodynamics from first principles.

Oxygen precipitation in Czochralski silicon heated in the range 400–1050°C is reviewed. For T≥525° C, Si02 particles form at the normal diffusion rate and there is generation of self-interstitials. At the lower temperatures, the existence of the interfacial energy causes an apparent increase in the solid solubility as the agglomerates become very small: at 525° C they contain only an estimated 20–50 atoms. A critical analysis s then presented of possible oxygen aggregation reactions at even lower temperatures when thermal donors are generated. It is not yet possible to reconcile the kinetics of these two processes, even if self-interstitials and/or vacancy reactions are included. There is no evidence for enhanced diffusion of isolated oxygen atoms except as a transient process occurring during the relaxation of stress-induced dichroism. Oxygen aggregation at 450 ° C appears to be limited by the formation of dimers with an activation energy of 2.5eV, while thermal donors form with an activation energy of 1.7eV.

Originally discovered in compound semiconductors, metastability is now being observed for many defects in silicon as well. Simple considerations indeed suggest the existence of alternate, metastable configurations for ab large variety of defect complexes, even as simple as ionic pairs. Techniques to isolate these excited defect configurations are also now well established, and being used routinely in a number of laboratories. This paper will review the recent achievements in this field. Selected examples will be described to illustrate the status of research on metastable defects in silicon.

Recent work on defect related phenomena in heterojunctions and quantum well structures is reviewed. These include situations in which quantum wells behave as deep traps and the use of shallow and deep centers as new tools for band structure engineering. Among the latter tunable band discontinuities and the artificial tailoring of superlattice states via δ-doping techniques are discussed.

Uniaxial stress perturbations have provided considerable data on the properties of optical centres in silicon. This paper reviews their uses in determining atomic kinetics and the symmetry of optical centres. Examples are given of the different effects of stress-induced interactions between states, and of the thermalisation of stress-split states. Uniaxial stresses are shown to be useful in grouping together similar optical centres, and in understanding the defect-induced widths of zero phonon lines and the vibronic properties of centres. At some optical centres, “internal” stresses can be used to contruct bound states from perfect crystal states.

A new type of bistable center is observed in electron-irradiated Si and identified as an interstitial carbon-substitutional carbon pair by combining several spectroscopic techniques. In the positive and negative charge states, the stable configuration of the defect involves a carbon-silicon interstitialcy (each atom 3-fold coordinated) next to a 4-fold coordinated substitutional C atom. In the neutral state, the defect rearranges its bonds so that both C atoms are substitutional (4-fold coordinated) with a 2- fold coordinated Si atom nestled between. Configurational coordinate energy surfaces are determined for each of the three charge states.

DLTS measurements are used to detect and identify the interstitial related defects in n-type silicon. The materials dependences of the reactions of the [E(0.12), H(O.27)], [ME(0.30), ME(0.29), ME(0.23), ME(0.21)], ]ME(0.10), ME(0.17)] and [H(0.36)] spectral features lead to their identification as representing the two charge states of Ci, the multistable configurations of Ps-Ci, the bistable Cs-Sii-Cs, and the Ci-Oi defects, respectively. The branching ratios for the reactions of interstitial carbon with the impurities are given.

The Si-G15 EPR spectrum and the 0.79eV “C-line” luminescence spectra in silicon are shown to arise from an interstitial carbon - interstitial oxygen complex. The g-tensor and 13C hyperfine interaction tensor indicate the structure in the vicinity of the carbon atom while stress alignment studies reveal the configuration near the oxygen atom. The pairing of the two impurities leads to a lattice relaxation which serves to stabilize the complex against dissociation.

Values of the diffusivity of silicon self-interstitials have been previously inferred from analyses of the in-diffusion of Au in undislocated Si, e.g., 2×10-7 cm2 s-1 at 1100 °C. A more complete analysis by numerical integration of the effective diffusion equation with fewer assumptions yields ahigher minimum value, 6×10-6 cm2s-1 at 1100 °C. Recently published experiments showing no measurable difference in the oxidation-reduced diffusion of Sb in Si at 10 and 40 microns are consistent with this high value.

Variable-energy positron beam studies have been made on ion implanted silicon. After 35, 60 and 100 keV H+ implantation a clear separation between vacancy and H atom distributions was found. In 100 keV As+ and P+ implanted Si the damaged layer extends to 300 and 400 nm, respectively, far beyond the the range of implanted atoms and the amorphous layer. Effect of thermal and laser annealing is also discussed.

The breathing mode (volume) lattice relaxations associated with carrier emission and capture are evaluated for a variety of deep levels in silicon using a recently proposed method based on high pressure measurements of the emission rates and capture cross sections. Included are 1) the vacancy-like acceptor levels associated with the oxygen-vacancy pair (or A-center) and the gold, platinum and palladium impurities, 2) the chalcogenide donors in their singly- and doubly-charged states and 3) a number of 3d transition metal donors. The signs and magnitudes (which range from -O to 5A 3/emitted carrier) of these relaxations are discussed in terms of models for the impurities and defects responsible for the associated levels. The results on the chalcogenides are compared with recent theoretical calculations.

We report a detailed study of the photoluminescence (PL) intensity of bound excitons (BE:s) in silicon, related to shallow impurities and deep complex defects, as a function of DC and high frequency AC (9GHz) electric fields. Two experimental approaches are presented. The first involves a simultaneous recording of PL and photocurrent under pulsed DC excitation. The second utilizes the optically detected cyclotron resonance (ODCR) technique, which allows detection of cyclotron resonance (CR) via the resonancetransition- induced changes of BE PL intensity. The mechanism responsible for the PL changes is shown to be the impact ionization of BE:s by hot free carriers. Effects of sample inhomogeneities in these experiments are also discussed.

Depth-dependent electrical characterization of epitaxial silicon extrinsically gettered with intentionally introduced misfit dislocations is described. To study the effect of buried defects on minority carrier lifetime, a modified Zerbst analysis of the MOS capacitance vs. time response was used to determine generation lifetime as a function of space charge region width. In addition, SEMEBIC imaging at different electron beam energies and EBIC imaging of cross-sections were used to investigate the depth-dependent electrical behavior of these materials.

The thermal stresses induced by temperature variations that exist during steady-state Czochralski growth produce plastic deformations in the crystal by dislocation motion and generation. The temperature variations in the crystal are calculated numerically by the finite element method (FEM). Employing the Haasen-Sumino viscoplastic response function for silicon and the calculated temperature profile, the thermal stresses, the dislocation densities, and the residual stresses in the crystal are also calculated. Only low dislocation densities are of interest and hence the associated viscoplastic deformations are found to be small. The assumption is made that there is a very low dislocation density along the solid-melt interface. The Haasen-Sumino material model is modified to include a back-stress to account for the locking effects due to the impurity concentration in the crystal. This analysis provides guidance for growing large diameter crystal of materials with known constitutive relations which have a low dislocation density and low thermal stresses.

The character of extended defects formed in high-energy S-ion implanted and rapid thermal annealed (RTA'd) Si has been found by transmission electron microscopy (TEM) to be dependent on the depth at which the defects have formed in the ion-implanted regions. Si implanted with 6 MeV S-ions and RTA'd at 1000°C for 10 s showed a buried layer of extended defects with unfaulted loops towards the top and faulted loops towards the bottom. At higher S fluences, all the loops were unfaulted, some loops coalesced to form a dislocation network, and SiS precipitates were formed. At higher RTA temperatures, all the loops were unfaulted. A few possibilities that could explain the difference in defect character will be discussed.

It is shown that indentation-induced formation of hexagonal silicon at the temperature range 400–700°C is fully consistent with its occurence via a martensitic transformation. After presenting HREM images of hexagonal ribbons in a diamond cubic matrix, a crystallographic analysis of the phase transformation is given, and a dislocation mechanism responsible for the transformation is discussed.

Recent absorption and photoconductivity studies of deep transition-metal impurities in silicon are discussed, with emphasis on optical transitions from the deep ground state to shallow Coulomb excited states. The P3/2 line spectra of the deep Au and Pt acceptors closely resemble those of group II acceptors in silicon, whereas the P1/2 lines show resonance effects due to interaction with the valence band continuum. Behavior under uniaxial stress is compatible with D2d or C 2y point-group symmetry for the Au and Pt acceptors. A line spectrum in g-dopes Si can be attributed to excitations to shallow donor states since the phononassisted Fano resonances involve characteristic inter-valley phonons. Both the Ag donor spectrum and the corresponding Au spectrum are dominated by excited s-state transitions. Thus, the traditional fingerprint of a donor in silicon, i.e. the effective-mass like p-state series, is missing or at best observed weakly

Deposition of Au on exsitu cleaned (100) Si wafers resulted in the formation of a discontinuous polvcrvstalline Au layer containing lattice defects. On parts of the interface Au and Si were separated by a thin oxide layer, but elsewhere were in direct contact, with no evidence of metastable phase formation. Post deposition heating to 1000°C. well above the 370°C eutectic temperature of the system, caused formation of a reaction zone at the interface, and disappearance of the thin oxide layer. No amorphous phases formed during cooling. Quenching produced small Au precipitates in Si-rich regions. If the wafer contained dislocations. Au precipitation was observed on subboundaries directly connected to the Au/Si interface, but not on dislocations remote from the interface.

An examination of Si+ pre-amorphised p+n structures as a function of Si+ implantation energy and solid phase epitaxial regrowth temperature has revealed three different classes of defect all of which may influence the characteristics of the junction. They are point defects responsible for high concentrations of deep level donors, and interstitial dislocation loops both causing leakage current degradation, and excess silicon interstitials leading to enhanced junction movement.