Study On The Structural And Magnetic Properties Of Fe (Cu) Doped Ⅳ-based Diluted Magnetic Semconductor Films

Si has been the most basic research material in the traditional semiconductor industry.Transition metal-doped group-IV semiconductors can be integrated with existing Si-basedmicroelectronic devices, so Si and Ge-based diluted magnetic semiconductors （DMSs） haveextensive value for the modern semiconductor industry. In recent years, Mn-doped groupIV-based DMSs have been extensively studied, but research on other transition metals （suchas Fe, Cu, Cr） has been comparatively less. In addition, the origin of the ferromagnetism isstill a topic in debate beacause there exist the disturbance of second phase in the samples.Considering that, we chose the transition elements Fe and Cu to dope group-IVsemiconductors by nonequilibrium growth method. The microstructure of the samples wascharacterized by much more accurate measurement in order to correctly evaluate theferromagnetism of the samples.1. Fe and N ions were co-implanted into Si wafers using the metal vapor vacuum arctechnique and Kaufman technique, prepare at room temperature and at673K, respectively.For the samples prepared at room temperature, X-ray absorption fine structure （XAFS）suggested that Fe ions existed in the matrix at isolated substitution sites in the low dosesample (2.0×10¹⁶cm^-2), while in the high dose samples of5.0×10¹⁶cm^-2and2.0×10¹⁷cm^-2,the non-ferromagnetic FeSi2phase formed. Magnetic measurements revealed that all thesamples showed room-temperature ferromagnetism. Due to the formation of FeSi2phase, thesaturated magnetization decreased with the increase of the implanted dose. Strengthening theeffect of the self-annealing can make for the formation of more FeSi2phase, which resulted inthe room-temperature ferromagnetism of the samples prepared at673K was weaker than thatof the samples prepare at room temperature. The origin of the ferromagnetism was from thesubstituted Fe ions randomly embedded in the Si matrix.2. A series of Si_1-xGe_x（x=1,0.848,0.591,0.382,0.209,0.064,0） thin films prepared byion beam sputtering were implanted with Fe ions to different doses using the metal vaporvacuum arc technique. XAFS was used to characterize the local microstructure around the Featoms in Fe-doped Si_1-xGe_xsamples. Structural analysis showed that for annealed samples of Ge-rich thin films （including pure Ge） implanted with low doses of Fe ions, almost all the Feions substituted at Ge sites. However, an anti-ferromagnetic Fe₆Ge₅impurity phase existed inthe annealed samples implanted with high doses of Fe. It was also found that the solubility ofFe ions was highest in pure Ge films and that with increasing Si concentration, the solubilitydecreased. Annealing was found to improve the solid solubility of Fe ions in Ge-rich thinfilms. Magnetic analysis showed that for the as-implanted and annealed samples of Ge-richthin films implanted with Fe ions, room-temperature ferromagnetism was strongest in thepure Ge series of samples and that as the Ge concentration decreased, the ferromagnetism atroom temperature weakened. In addition, annealing could increase the number of Fe ions atsubstitution sites, which resulted in the observed increase in the saturated magnetizationafterannealing. Experiment and theoretical analysis showed that the ferromagnetism ofFe-doped Ge-rich Si_1-xGe_xthin films samples originated from the s, p-d exchange interactionsbetween the Si_1-xGe_xmatrix and those Fe ions which substituted at Ge sites and that theferromagnetism was mediated by carriers.3. Thin films of Si_0.791Ge_0.209and Si_0.773Ge_0.204C_0.023were prepared by ion beamsputtering and were implanted with Fe ions to different doses using the metal vapor vacuumarc technique. XAFS was used to characterize the local microstructure around the Fe atoms inthe Fe-doped Si_0.773Ge_0.204C_0.023samples. Structural analysis showed that in theSi_0.773Ge_0.204C_0.023films implanted with low doses of Fe ions, almost all the Fe ions substitutedat Ge sites. However, an anti-ferromagnetic Fe₆Ge₅phase existed in the samples implantedwith high doses of Fe. On the other hand, in Fe-doped Si_0.791Ge_0.209samples, the Fe₆Ge₅phasewas present even when the lowest dose was implanted. We found that the introduction of theC was conducive to the improvement of the lattice matching degree between matrix and Sisubstrate, to the Fe ions preferentially residing at substitution sites and to the effectivesuppression of the formation of impurity phases. Magnetic analysis showed that theroom-temperature ferromagnetism of Fe-doped Si_0.773Ge_0.204C_0.023samples was clearlystronger than that of the Fe-doped Si_0.791Ge_0.209samples. The intrinsic ferromagnetism of theimplanted samples originated from the substituted Fe ions embedded in the matrix, and wasmediated by charge carriers. 4. Silicon semiconductor samples implanted with Cu ions and samples co-implanted withCu and N-ions were prepared by MEVVA and the Kaufman technique. None of the samplesshowed evidence of secondary phases. The initially n-type Si matrix, when implanted with Cuions, changed to a p-type semiconductor, and the Cu ions existed as Cu+in the p-typeenvironment. As a result, none of the Cu-implanted samples were ferromagnetic at roomtemperature. The co-implanted samples, on the other hand, showed room-temperatureferromagnetism because the introduction of N ions made the carrier type change from p-typeto n-type which is favorable for the appearance of Cu²⁺. The room-temperatureferromagnetism of the Cu and N co-implanted samples originated from the exchangeinteractions between of the Cu²⁺ions, mediated by electron carriers.