Oxygen-Atom Defects In 6H Silicon Carbide Implanted Using 24- MeV O[sup 3+] Ions Measured Using Three-Dimensional Positron Annihilation Spectroscopy System (3DPASS)

Abstract

Three dimensional electron‐positron (e−‐e+) momentum distributions were measured for single crystal 6H silicon carbide (SiC); both virgin and having implanted oxygen‐atom defects. 6H SiC samples were irradiated by 24‐ MeV O3+ ions at 20 particle‐nanoamps at the Sandia National Laboratory’s Ion Beam Facility. O3+ ions were implanted 10.8 μm deep normal to the (0001) face of one side of the SiC samples. During positron annihilation measurements, the opposite face of the 254.0‐μm thick SiC samples was exposed to positrons from a 22Na source. This technique reduced the influence on the momentum measurements of vacancy‐type defects resulting from knock‐on damage by the O3+ ions. A three‐dimensional positron annihilation spectroscopy system (3DPASS) was used to measure e−‐e+ momentum distributions for virgin and irradiated 6H SiC crystal both before and following annealing. 3DPASS simultaneously measures coincident Doppler‐broadening (DBAR) and angular correlation of annihilation radiation (ACAR) spectra. DBAR ratio plots and 2D ACAR spectra are presented. Changes in the momentum anisotropies relative to crystal orientation observed in 2D ACAR spectra for annealed O‐implanted SiC agree with the local structure of defect distortion predicted using Surface Integrated Molecular Orbital/Molecular Mechanics (SIMOMM). Oxygen atoms insert between Si and C atoms increasing their separation by 0.9 Å forming a Si‐O‐C bond angle of ∼150°.