G. D. Watkins

Intrinsic defects in silicon

Abstract A review is given of what has been learned from electron paramagnetic resonance (EPR) and localized vibrational mode (LVM) spectroscopy concerning isolated lattice vacancies and self-interstitials, and their interactions with other defects in silicon. This information can supply the basic tools with which to help unravel much of the complex processes and structures involved in crystal growth, device processing, and radiation damage.

Native Defects and their Interactions with Impurities in Silicon

A review is given of what has been learned from EPR studies over the last ∼35 years concerning vacancies and interstitials in silicon. Lattice vacancies are well understood, their diffusional migration energies determined vs charge state and electronic excitation, and their interactions with most of the common impurities established. The isolated interstitial has not been observed by EPR but a great deal has been learned concerning it from studies of its interactions with impurities, and more recently from theory. The properties of these two intrinsic defects and their progeny will be analyzed to help clarify their role in both the normal thermally activated diffusion processes and the transient-enhanced ones, which are of particular current concern.

Origin of the 0.97 eV luminescence in irradiated silicon

Abstract Optical detection of magnetic resonance studies are described for the well-studied optical center with zero phonon line at 0.97 eV in irradiated silicon. Analysis of the S=1 ODMR spin Hamiltonian reveals a low symmetry (C lh ) center and a resolved 29 Si hyperfine interaction with a single silicon atom. In a specially enriched 13 C doped sample we find additional hf interactions with two equivalent carbon atoms. At elevated temperatures, the defect reorients easily from one C lh distortion to another around a common 〈111t> axis; during this reorientation the spin density remains located on the same silicon atom and the same carbon pair. From these results we construct a model comprising two adjacent (substitutional) carbon atoms and an interstitial silicon atom which has distorted out from a bond-centered position. We conclude that the same defect gives rise to the Si-G11 EPR spectrum when positively charged.

Diffusion of oxygen in silicon

Recently reported measurements of oxygen diffusion in silicon agree within experimental accuracy with a previous estimate D=0.23 exp(−2.561±0.005 eV/kT) cm2 s−1, determined from a direct measurement at lower temperatures of the one‐jump process for interstitial oxygen from one Si‐Si bond to an adjacent one. The diffusion constant is therefore known over 11 decades and results from a single microscopically identified process. There are few such model textbook examples for diffusion in solids.

The vacancy in silicon : Identical diffusion properties at cryogenic and elevated temperatures

The vacancy contribution to self-diffusion in silicon, recently revealed in the study by Shimitzu et al. [Phys. Rev. Lett. 98, 095901 (2007)], is analyzed to demonstrate that the pre-exponential term, as well as the enthalpy term, matches accurately to that of the isolated neutral vacancy, as determined many years earlier at cryogenic temperatures by electron paramagnetic resonance and deep level transient spectroscopy. The persistent suggestion of an “extended” vacancy with very different migrational properties at elevated temperatures is therefore incorrect. There is only one vacancy.

Metastable defects in silicon: hints for DX and EL2?

A review is given of defects that display metastability in silicon, with emphasis on those that have been identified and the various mechanisms that they reveal for the phenomenon. Pair defects described include interstitial-iron-substitutional-group-III-acceptors and ones formed by interstitial carbon with substitutional group V donors or substitutional carbon. Interstitial hydrogen, boron and silicon and substitutional nitrogen and oxygen are taken as examples of isolated single-atom defects that display on-centre to off-centre instabilities. It is argued that this single-atom instability can be understood in terms of a predictable Jahn-Teller effect and that this concept may provide useful insight into the DX and EL2 phenomena in the III-V materials and their alloys.

Optically detected electron paramagnetic resonance of arsenic antisites in low-temperature GaAs layers

Arsenic antisites in GaAs layers grown by molecular‐beam epitaxy at low substrate temperatures (∼200 °C) were observed using electron paramagnetic resonance (EPR), magnetic circular dichroism in absorption (MCDA), and MCDA‐detected EPR. This observation confirms that there is a MCDA band directly associated with arsenic antisites in the GaAs layers.

Deep levels in semiconductors

Abstract The 3d transition element ion impurities in silicon are reviewed for the broad insight they provide in understanding deep levels in semiconductors. As interstitials, their interaction with the host tends to confine the d-levels to the forbidden gap, providing many deep states. The interaction at the substitutional site is best considered as an interaction with the lattice vacancy, into which the impurity is placed. This interaction tends to repel deep a1 and t2 levels from the gap. When the levels are present, they are mostly vacancy-like and the defect is likely to display the large lattice relaxations characteristic of the vacancy.

ODMR studies of antisite-related luminescence in GaP

Abstract By the use of ODMR, we have detected and identified two different antisite defects which contribute to newly-reported infrared luminescence observed in GaP. The antisite proper, PGa, gives rise to a spin- 1 2 resonance; the associated luminescence originates in the DA pair recombination of an electron trapped at the deep double donor P+Ga with a distant shallow acceptor. An impurity-associated centre of the form PGa · YP is observed in a spin-triplet state via a distinct luminescence band which originates in electron-hole recombination localised at the defect.

Alignment of thermal donors in Si by uniaxial stress

Thermal donors generated in Czochralski‐Si by heat treatment at around 450 °C can be preferentially aligned by applying a large uniaxial stress during their formation process. This alignment is clearly observed by a polarization of the optical transitions of the thermal donors and a corresponding effect for the paramagnetic NL8 centers. Thus a strong correlation between thermal donors and NL8 is again demonstrated, as well as the extended defectlike nature of such defects. The g3 value of the g tensor and the 2p0 dipole oscillator are found to be oriented preferentially perpendicular to the stress direction, a result which seems to disagree with some of the presently discussed thermal donor models.