Semiconducting FeSi2 has attracted considerable amount of research interest in the past decade for its potential applications as a silicon-based light emitting material. In this work, FeSi2 precipitates were formed in Si by iron implantation into silicon using a metal vapor vacuum arc ion source. The structures and light emitting properties of these ion-beam-synthesized FeSi2 precipitates were studied in details using various characterization techniques, including transmission electron microscopy (TEM) and photoluminescence measurements. It was found that the implantation temperature played an important role on the dislocation loop formation and hence the FeSi2 phase formation during the subsequent thermal annealing. Photoluminescence (PL) spectra were measured as a function of temperature from 80 to 300 K. Combining the TEM and PL results, the origins of the PL could be distinguished to be either from the defect-related emission of Si or from the FeSi2 precipitates. The FeSi2 precipitates were found to be highly-strained or relaxed depending on the implantation and annealing conditions. The band gap energy of the relaxed samples was determined to be about 11 meV higher than that of the highly strained samples. Simple metal-oxide-semiconductor (MOS) diode structures were fabricated to study the electroluminescence (EL) properties from this FeSi2/Si system. Preliminary results showed that clear EL signals were obtained even at room temperature for samples prepared at appropriate conditions. There are significant differences between the EL and PL spectra and the mechanisms of the EL emission has yet to be further investigated.
In this work, TiO2 thin films were prepared by RF sputtering onto thermally grown oxide layers on Si substrates. Cobalt and iron implantation into the TiO2 films was performed using a metal vapor vacuum arc ion source. The as-implanted and annealed films were characterized using Rutherford backscattering spectrometry, transmission electron microscopy, x-ray diffractometry, x-ray photoelectron spectroscopy, spectroscopic ellipsometry, and vibrating sample magnetometry. The dependence of the magnetic properties on the implantation and annealing conditions were studied in detail. Clear room temperature ferromagnetic properties (RT FM) were observed. The saturation magnetization (Ms) values per implanted Co or Fe atom exhibit an oscillatory dependence on the implantation dose. The maximum Ms in one Co implanted samples was determined to be 2.3 μB/Co, exceeding the bulk Co value. The possible origins of the RT FM properties are discussed.