Study On The Properties Of Fe(Cu,Cr) Doped Ge(Si) Based Diluted Magnetic Semconductor Films

Diluted magnetic semiconductor (DMS) has attracted considerable attention as a foundation of spinstronics over recent years. Researchers hope that the conventional semiconductor can be improved by control the electron spin in semiconductor. It has been suggested that DMS will be the base of nonvolatile memories with high data processing speed and low power consumption.In recent years, much work has been done, and plenty of satisfactory results have been achieved. However, the origin of the ferromagnetism observed in DMS materials has not been clear. Therefore, in this work, Fe (Cu, Cr) doped Ge (Si) DMS films were prepared by ion beam implantation and magnetron sputtering method. The influence on the thin films properties which is caused by co-doping, different type of carriers, and different matrix have been studied.Firstly, Fe doped Ge films were prepeared by ion beam implantation and ion beam sputtering. The dose of Fe were 3×10¹⁶/cm² and 4×10¹⁶/cm² respectively. Then N ions were implanted to the prepared films, the influence of N on the thin films properties has been discussed. The study of the structure and magnetism shows that introduction of N in Fe:Ge films can extinguish the Fe₃Ge₂ ferromagnetic particles in the films, and the ferromagnetism observed in the co-doped films is intrinsic property. The electron transport properties of these samples is consistent with the variable range hopping model, the ionization energy of samples were reduced after the introduction of N in Fe:Ge films.Secondly, Cu ions were implanted in n-Si and P-Si respectively, and then the influence of the different type of carriers in matrix was studied. The result shows that Cu doped P-Si films are diamagnetic at room temperature. However, the Cu doped n-Si films show weak ferromagnetism at room temperature, the saturated magnetization is decreased with increasing dose of Cu. It is related to the precipitation of Cu particles and antiferromagnetic exchange interaction between Cu²⁺. The ferromagnetism arise from the interaction between Cu²⁺ of the sample is the sample's intrinsic property. The results of the experiment to test electric properties show that the charge transport mechanism of these films is consistent with the Efros-Shklovskii variable range hopping model. The study of electric properties proved the origin of the ferromagnetism on the other hand.Thirdly, Cr:Ge, Cr:Si films are prepared by magnetron sputtering and anneal method. We combine X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS) to analyse the microstructure of the films. The result showed that the Cr atoms in Cr:Ge films are situated in substitutional sites, well the Cr atoms in Cr:Si situated in substitutional sites when the concentration of Cr is low (8%), the number of interstitial Cr increased with increasing Cr concentration. Experimental study showed that Cr atom prefer to situate in the substitutional sites in Ge matrix rather than in Si matrix. Theoretical calculation result by material studio is the same as the experiment result above.