Positron annihilation and the charge states of the phosphorus-vacancy pair in silicon

Abstract

After electron irradiation two positron lifetimes 250+or-1 and 268+or-3 ps, are observed in phosphorus-doped Si ((P)=3*1016 cm-3) depending on the temperature and the electron fluence. The lifetimes are assigned to the negative and neutral charge states of the phosphorus-vacancy pair (P-V). The longer lifetime at the neutral charge state indicates a larger open volume of the vacancy and implies an outward relaxation of the phosphorus-vacancy pair in the charge-state transition (P-V)- to (P-V)0. A comparison with the theoretical lifetimes yields a breathing-mode relaxation of the nearest-neighbour atoms Delta r/r0 approximately 5.1% (r0 is the Si-Si bond length), or Delta r approximately 0.12 AA. The positron trapping coefficients 2*1016 s-1 at 20 K and 2*1015 s-1 at room temperature at the negatively charged state (P-V)- are estimated. A weakly bound Rydberg-like precursor state is invoked to explain the temperature dependence of positron trapping at the negatively charge centres (P-V)- and V- in Si. The binding energy at the precursor state is 15-30 meV.

Identification of Vacancy-Impurity Complexes in Highlyn-Type Si

“…When the vacancy concentration exceeds 10 18 cm 23 [5,10], all positrons annihilate at the irradiation-induced vacancy defects with the lifetime 247 6 2 ps, and no annihilations take place at the delocalized bulk state or at the native vacancies detected only before irradiation. The vacancy concentration of ϳ10 18 cm 23 is consistent with the expected introduction rate in electron irradiated heavily n-type Si [10][11][12]. We checked with electrical measurements that the conductivity of the samples remains practically unchanged in the irradiation, indicating that the concentration of electrically active As is much larger than that of vacancies.…”

“…The same positron lifetime at the vacancy, t V 248 6 3 ps, is thus observed for three different types of samples: [10,11] and theoretical calculations [13], the lifetime of 248 6 3 is typical for the single vacancy in Si, whereas for a divacancy much larger values of about 300 ps are observed [13][14][15]. In all three systems listed above, the open volume of the dominant vacancy defect is the same, and equal to that of a monovacancy.…”

Momentum distributions of electron-positron pairs annihilating at vacancy clusters in Si

“…We will compare our results with those of the previous study by Saito and Oshiyama 11 and with the experimental data. 25,31,32 The defects have been calculated in the neutral charge state. Actually, the charge state would affect the positron parameters mainly through the ionic relaxation, 26,27 so that in our calculations ignoring the relaxation the charge state is not an important parameter.…”

Convergence of supercell calculations for point defects in semiconductors: Vacancy in silicon

“…Positron lifetime measurements have given information about the open volume changes for the vacancyphosphorus pair in Si when the charge state of the defect changes. 6 Also DLTS has been used for this purpose. 7 Watkins has described the electronic and ionic structure of the vacancy in Si on the basis of the linear combination of atomic orbitals ͑LCAO͒ model.…”