Symmetry and Nature of the 1.0186 eV Luminescence Centre in Neutron ‐ Irradiated Silicon

Abstract

Irradiation of silicon crystals by high-energy electrons, f -rays, neutrons, o r ions is known to lead t o the generation of radiation defects which cause the appearance of a number of electron-vibrational bands in luminescence spectra /1 to 4/. The presence of narrow zero-phonon emission lines in these spectra permits an effective use of uniaxial s t r e s s effects for determining the symmet r y of the corresponding luminescence centres /5/. Knowledge of this important microscopic characteristic is, in most cases, a decisive factor for the choice of geometrical and physical models and ultimately for the establishment of the irradiation-induced defect nature.The luminescence band with the zero-phonon line at 1.0186 eV has been observed in pulled and float-zone silicon crystals after irradiation by neutrons /3/ and various ions /2, 4/ and annealing in the temperature range 50 to 350 OC. Previously /2/, the centres responsible for this band, considering the apparent impurity independence, annealing properties, and comparison with the E P R data, have been tentatively identified with the five vacancy cluster defects (Si-P1 centre),which have Clh(= Cs) symmetry /6/.In this note we report the results of uniaxial stress studies on the 1.0186 eV emission line performed with the purpose to determine the symmetry of the corresponding centres. F r o m the analysis of uniaxial s t r e s s splitting of the line and the relative intensity of the stress-split components under a polarized light, it is found that the centres have a trigonal symmetry with a circular magnetic dipole oscillator in the plane normal to the (111) centre axis. The preliminary data of these investigations have been reported in /?/.

New Class of Related Optical Defects in Silicon Implanted with the Noble Gases He, Ne, Ar, Kr, and Xe

“…This spectrum was previously investigated in several independent works 7 " 10 ; it was found that the spectrum depended neither on the donor or acceptor doping of the starting material nor on the persistent impurities carbon or oxygen, and it was observed after high-energy neutron irradiation of Si, 7 after ion implantation (irrespective of the ion species) and thermal 8,10 or laser annealing, 11 or in neutron-transmutation-doped (NTD) unannealed Si regardless of the neutron dose and energy. 12 The underlying defect is obviously intrinsic and was tentatively identified 8,9 with the EPR Si-Pi center (a nonplanar five-vacancy cluster of C\ h symmetry 13,14 ) or recently, on the basis of a trigonal symmetry classification, 15 with the EPR Si-^3 center (a trigonal tetravacancy clus- ter 14 ) or a (111) Si split interstitial.…”

“…Line 9 shows no isotopic shift in the I x spectrum from selectively 13 C-enriched material, demonstrating that it is not related to carbon which is known to be mainly responsible for vibronic line shifts of 71.9 meV ( 12 C) or 69.85 meV ( 13 C) in the G (0.97-eV) defect spectrum. 3,4 Applying uniaxial stress, Minaev, Mudryi, and Tkachev 15 have recently shown that the I\ defect has trigonal symmetry and that the NP transition corresponds to a IT oscillator with the piezospectroscopic tensor element A x = -0.04 meV/GPa and ^2 == 0-22 meV/GPa. Our stress experiments (up to 0.5 GPa) are consistent with these data for I Xi and exhibit similar splittings of the Ar and Kr NP lines into one, two, or two components under (100), (111), or (110) stress, respectively.…”

Some new photoluminescence features of W line for neutron-irradiated MCz-Si and FZ-Si

“…It leads to the larger number of free holes and electrons that can be captured by deeper centres and higher intensity of PL emission related to these centres. The equation (2) is responsible for taking into consideration this assumption in (1). The slow decrease of the W line intensity between 15 K and 35 K can be obtained by fitting procedure when it is assumed that as the temperature is on the rise, the probability of the occupation of the ground states of exciton species decreases.…”

“…The defect consists of three interstitial silicon atoms inserted into the bond centres of three neighboring bonds parallel to <111> direction. Trigonal symmetry of the defect related to W line was confirmed experimentally [1], [3]. Electron spin resonance (ESR) study for neutron-irradiated silicon [7] provides the evidence for linking the paramagnetic B5 centres to the W optical centres.…”

Growth of Precursors in Silicon Using Pseudopotential Calculations

“…2(b). These properties of J ͑1͒ 5 make this model a possible candidate for optically active W centers, which possess the symmetry of the point group C 3y with symmetry axis along ͗111͘ direction [25]. An alternative tri-interstitial model, which comprises three bondcentered interstitials with fully saturated bonds, was recently proposed as the candidate for W center in silicon [26].…”