Acceleration of Diffusional Jumps of Interstitial Fe with Increasing Ge Concentration in Si1 − x Ge x Alloys Observed by Mössbauer Spectroscopy

Abstract

Radioactive 57 Mn isotopes have been implanted into Si 1jx Ge x crystals (x e 0.1) at elevated temperatures for Mössbauer studies of the diffusion of interstitial 57 Fe daughter atoms. The atomic jump frequency is found to increase upon Ge alloying. This is attributed to a lowering of the activation energy, i.e. the saddle point energy at hexagonal interstitial sites with Ge neighbour atoms.

57Fe Mössbauer investigations in p-type Silicon Germanium single crystals

“…Figure 4B clearly shows that the activation energy decreases with Ge alloying which contributes significantly to the increase of the jump frequency with increasing Ge concentration. A similar trend was observed by Weyer et al [7] for n-type SiGe materials however their activation energy of 0.89 eV for Si 0.96 Ge 0.04 is much higher than our results. This is not unexpected because of the faster diffusion of Fe + I relative to Fe 0 I .…”

“…At temperatures above 600 K, the spectral component assigned to Fe I -V pairs dominates the spectra. These results are similar to those obtained by Gunnlaugsson et al [6] for Si and Weyer et al [7] for n-type Si 1−x Ge x (x ≤ 0.10).…”

“…Diffusivity of interstitial Fe I in p-type Si 1−x Ge x single crystals has been measured by monitoring the line broadening of the interstitial line in 57 Fe Mössbauer spectra obtained after implantation of radioactive 57 Mn in the temperature interval from 450-600 K. The results show the accelerated diffusion of interstitial Fe with increasing Ge content similar to those obtained for n-type SiGe [7]; however the activation energy obtained for the n-type material is much higher than our results because of the faster diffusion of Fe + I relative to Fe 0 I . Further, the activation energy obtained in this study for Fe diffusion is much lower than for As [13], Sb [14] and Sn [15] in relaxed SiGe, attesting that Fe is a fast diffuser in SiGe (and in Si).…”

“…Recently Gunnlaugsson et al [6] observed that the diffusivity of Fe + I is larger than that of Fe 0 I for P-and B-doped Si materials, respectively, and found that their results are compatible with those obtained by Heiser and Mesli [2]. In a latest study, Weyer et al [7] observed that the atomic jump frequency to increase with Ge alloying in n-type Si 1−x Ge x (x < 0.1), which was ascribed to a lowering of the activation energy. In this contribution, we report on the diffusion characteristics of interstitial Fe with increasing Ge concentration (x) in p-type samples, observed by 57 Fe Mössbauer spectroscopy and show that Fe + I diffuses faster than Fe 0 I in SiGe crystals.…”

“…A decrease of the Fe I energy in such a hexagonal saddle point configuration then corresponds to a decrease of the activation energy and would explain an increase in the jump frequency for such a direction. A more detailed discussion of the atomic jumps in such a model is given by Weyer et al [7].…”