Defect formation in Mn-implanted silicon probed by frequency and temperature dependent capacitance measurements on MOS capacitors

In order to obtain magnetic Si the doping of it by Mn is one of the topics in this field. This opens the possibility to fabricate Si-based spintronic devices. Most of the research activities focused on material science, e.g. reporting higher Curie temperatures, and on characterizing their structural properties. However exploring the electrical properties after Mn doping is also important, so that the knowledge can be directly transferred to spintronic device fabrication. In these devices, an MIS (metal-insulator-semiconductor) structure is usually used and a high-quality oxide-semiconductor interface is therefore highly demanded. In this contribution, we investigate the defects in Si and in the interface between SiO2 and Si after the doping by Mn implantation into both p-type and n-type Si wafers. The implantation energy was 60 keV with a fluence of 2×10^15 cm^-2, resulting in a peak concentration of 5×10^20 cm^-3. A 15 nm thick SiO2 layer was grown during subsequent thermal oxidation at 900 °C. After this thermal treatment, the Mn atoms are solved in the Si wafer and partially in the SiO2 layer. Additionally, Mn in the region of the implanted profile with a nominal concentration above the solubility limit causes the formation of Mn-silicide nanoparticles [1]. The quality of SiO2/Si interface was checked by frequency dependent CV measurements. A large amount of defects was found at the SiO2/implanted-Si interface. Temperature dependent capacitance transient measurements reveal the formation of deep traps in the implanted Si, with energies of EV+0.54 eV, EV+0.41 eV in p-Si, and EC-0.57 eV, EC-0.23 eV, EC-0.11 eV in n-Si, respectively. All these electrical defects have to be considered when fabricating transition metal/SiO2/Mn-implanted Si structures for spin-dependent tunnelling devices.

[1] Shengqiang Zhou et al., Phys. Rev. B 75, 085203 (2007)