Evaluation of some basic positron-related characteristics of SiC

Abstract

First-principles electronic structure and positron-state calculations for perfect and defected 3C-and 6H-SiC polytypes of SiC have been performed. Monovacancies and divacancies have been treated; the influence of lattice position and nitrogen impurities have been considered in the former case. Positron affinities and binding energies have been calculated; trends are discussed, and the results compared with recent atomic superposition method calculations. Experimental determination of the electron and positron work functions of the same 6H-SiC allows an assessment of the accuracy of the present first-principles calculations, and to suggest further improvements. ͓S0163-1829͑96͒01828-0͔

Ferromagnetism in proton irradiated 4H-SiC single crystal

“…30 When a positron is implanted into solids, it annihilates with an electron and emits two 511 keV γ quanta. 31 The energy distribution of annihilation γ rays is broadened and can be expressed in Doppler shift.…”

Positron annihilation spectroscopy investigation of vacancy defects in neutron-irradiated3C-SiC

“…Two identical 5×5×1mm disks were sectioned from the original sample by using a low-speed diamond saw. The samples used for PAS measurements had a conventional sample-source-sample geometry and were prepared by directly evaporating a 20μL Na 22 Cl solution (~3.7×10 5 Bq) onto the surface of one of the two disks and, after the water evaporated, then covering that disk with the other disk. This "sandwich" was then wrapped in 10μm thick aluminum foil.…”

“…However, information on the sizes and concentrations of vacancy clusters in SiC cannot be determined from these techniques. In contrast, positron annihilation spectroscopy (PAS) is a well-established tool for investigating open-volume defects in condensed materials [16], and has been extensively employed to characterize the vacancy-type defects in as-grown [17,18] [19] or irradiated SiC [20][21][22][23] [19,[24][25][26]. Positron annihilation lifetime spectroscopy (PALS) is most commonly used to identify the sizes and concentrations of the vacancy clusters present within the materials.…”

Clustering of vacancy defects in high-purity semi-insulating SiC

“…8,[14][15][16]18,[20][21][22] The theoretical calculations give lifetimes of 134 ps for 4H-SiC, 23 141 ps for 6H-SiC, and 138 ps for 3C-SiC. 11 It should be noted that different calculation schemes ͑especially different enhancement factors͒ cause differences in the resulting absolute lifetimes, which become evident when comparing results from different studies. 23 A somewhat similar situation applies to experimental values ͑e.g., due to differences in measurement geometry, energy windows, or source corrections͒.…”

“…[8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] ͒. These studies often involve irradiated materials.…”