Acceptor-Donor pairs in semiconductors like Si and Ge have been thoroughly studied by Wichert et al. [1] and Forkel et al. [2]. In view of recent theoretical calculation of the electric field gradient (EFG) present at the probe 111In site of such pairs in Si and Ge [3], it is interesting to study the behavior of these complexes under mechanical stress. The samples used were cut along ⟨110⟩ crystal axes from a 100 μm thick Si wafer with ⟨110⟩ surface orientation. The 75As donor in Si was implanted to the samples with doses of 4·1014/cm2 and 1·1016at/cm2, at an energy of 160 keV and then annealed at 1173 K under a vacuum of p∼10−5 mbar. The 111In was implanted with an energy of 160 keV and annealed in the same way.
PAC measurements were carried out in two phases. In the first step, measurements were taken without stress, which was designed to see whether the expected pairs were formed in the samples or not. In the sample with an As dose of 1·1016at/cm2, 87% of the probe nuclei formed the expected pairs. The fit to the data showed that 51% of the probe nuclei form InAs1 pairs(site1) and 36% form InAs2 pairs(site2) characterised by unique interaction frequencies 229(1) MHz and 239(1) MHz, respectively. The remaining fraction of the probes remain in undisturbed position. The asymmetry parameters obtained η=0.00 for site1 and η=0.65 for site2 are consistent with the previous study [1].
In the second step, PAC measurements were taken under the influence of uniaxial stress along the ⟨110⟩ direction. In these measurements in addition to those interaction frequencies associated with the pairs, a tension induced frequency is also observed. Uniaxial tensile stress produced by bending the sample to the bending radius of 43 mm, which corresponds to a pressure (1.9kbar), yields interaction frequencies for the pairs of 229(2) MHz and 245(1) MHz for site1 and site2, respectively. Those probe nuclei, which do not trap defects saw of tension induced frequency of 20(1)MHz for the chosen stress.
This and other measurements using lower As dose under uniaxial stress showed that the interaction frequency for InAs1 remains essentially unaffected by the stress even at the highest stress of 2.1 kbar. A slight increase of ∼6(1)MHz has been observed for site2 (InAs2), indicating that this site , where the two As atoms preferentially take the next nearest position along ⟨110⟩ direction, is affected by the application of uniaxial stress along ⟨110⟩ direction.
[1] Th. Wichert and M.L. Swanson, J. Appl. Phys. 66 (1989) 3026
[2] D. Forkel, N. Achtziger, A. Baurichter, S. Deubler, M. Puschmann, H. Wolf and W. Witthuhn, Nucl. Instr. Meth. B63 (1992) 217
[3] M. Settels, T. Korhonen, N. Papanikolaou, R. Zeller and P.H. Dederichs, Phys. Rev. Lett. 83 (1999) 4369
[4] G. Marx, Doctoral thesis, Rheinische Friedrich-Wilhelms-Universität Bonn, (1995)
[5] G. Marx and R. Vianden, Hyperfine Interactions 97–98 (1996) 211