An electron paramagnetic resonance study was made of new defects (Si-AA15, Si-AA16) which incorporated Al atoms. The AA15 defect was created in H-doped material by low-temperature (about 80K) irradiation. The observation of 27Al hyperfine interaction revealed the presence of 2 almost equivalent Al atoms. In contrast to the case of Ali-Ali pairs (G19, G20), Al atoms which were incorporated into the AA15 defect had similar hyperfine parameters. Both Al atoms were nearly equivalent. It was therefore deduced that the Al atoms were placed in interstitial positions which would be equivalent in a perfect lattice; but an additional slight distortion reduced the symmetry to C1h, and resulted in a non-equivalence of the atom positions. The distortion was suggested to be a consequence of the Jahn-Teller effect or a result of the presence of an additional defect that was close to one of the Al atoms. It was possible that this perturbing entity might be a H atom. The appearance of the AA15 defect, which contained an Al-Al pair, was the first indication of the H-enhanced long-range migration (at least 100 lattice constants) of Al atoms at temperatures below 200K. The AA15 center annealed out at room temperature. The AA16 center, which contained only one Al atom, disappeared at 200K. Tentative models were proposed, for the AA15 and AA16 defects, which assumed that they were Al-Al <110>-split interstitials and Al-H interstitial pairs, respectively.

Al–Al Pair in Silicon - Evidence for Long-Range Hydrogen-Enhanced Aluminium Migration. K.A.Abdullin, B.N.Mukashev, J.V.Gorelkinskii: Applied Physics Letters, 1997, 71[12], 1703-5

Figure 2

Diffusion of Al in Si