Positron–electron autocorrelation function study of E-center in silicon

Abstract

Two-dimensional angular correlation of annihilation radiation ͑2D-ACAR͒ spectra have been taken for 10 19 cm Ϫ3 phosphorus-doped Si in the as-grown state after having been subjected to 1.8 MeV electron fluences of 1ϫ10 18 and 2ϫ10 18 cm Ϫ2. Positron annihilation lifetime spectroscopy confirms, in accordance with previous works, that positrons are saturation trapping into (V Si :P) pair defect ͑E-center͒ monovacancy sites in the electron irradiated samples. In the as-grown case, the positron-electron autocorrelation functions along the ͓111͔ and ͓1-10͔ directions, obtained through Fourier transformation of the 2D-ACAR data, reveal zero-crossings that deviate only slightly from the lattice points, in a manner consistent with positron-electron correlation effects. Conversely, in the spectra of the irradiated samples, the zero-crossing points are observed to move outward further by between 0.15 and 0.50 Å. This displacement is associated with positron annihilation with electrons in localized orbitals at the defect site. An attempt is made to extract just the component of the defect's positron-electron autocorrelation function that relates to the localized defect orbitals. In doing this features are found that correspond to the expected atomic positions at the vacancy defect site suggesting that this real-space function may provide a convenient means for obtaining a mapping of localized orbitals. The observed approximate separability of positron and electron wave-function autocorrelates leads to an estimate of 0.22 eV for the positron binding energy to the E-center.

Positron annihilation spectroscopic study of hydrothermal grown n‐type zinc oxide single crystal

“…Momentum distribution of annihilation radiation obtained from 2D angular correlation of annihilation raidaiton (2D-ACAR) and coincident Doppler broadening spectroscopy (CDBS) have been proved to be a valuable method to identify vacancy type defects [15][16][17][18][19][20][21]. The observable 2D-ACAR spectrum is given by:…”

Silicon and carbon vacancies in silicon carbide studied by coincidence Doppler broadening spectroscopy

“…The ACF of a crystalline solid provides lattice information from its zero crossing position [4]. This is also largely true for the ACF of a positron trapped in vacancy defects since the positron samples the valence electrons that have close to crystalline wavefunctions [5]. The FLAPW first principle calculated ACF for as-grown un-defected SiC (0001) as shown by the solid line in Fig.…”