Study On The Growth,morphology And Magnetism Of Mn_xGe_1-x/Si Quantum Dots Prepared By Ion Beam Co-sputtering

Hetero-epitaxial MnxGe1-x/Si quantum dots diluted ferromagnetic semiconductors have aroused enormous interests because of its compatibility with current Si microelectronics and the possibility to possess higher Curie temperature(Tc)than those of group ?-? materials.At the end of the last century,the advent of ultra-high vacuum molecular beam epitaxy(UHV-MBE)made the preparation process of high-performance dilute magnetic semiconductor materials to a new height.Nowadays,research work has been carried out extensively including II-V.II-VI,IV-VI and III-V compounds.However,the preparation of MnaGe1-x/Si quantum dot thin film materials by ion beam sputtering(IBS)is still rarely reported.Due to the advantages of low cost,simple operation and high performance,ion beam sputtering is still the object of choice for many research groups compared with MBE.In this paper,we combine ion beam co?sputtering with the experience of the group's years of growing Ge/Si quantum dots?six Mn,Ge,_x/Si quantum dot samples with different Mn doping concentrations were successfully fabricated on a P-type resistive Si(001)substrate.The details are as follows:1.Using the convenience of orthogonal experiment and controlled variable method,the optimal parameter combination of MnXGei1-x/Si quantum dot growth with high density,size and spatial uniformity is explored.That is,after growing a 50 nm Si buffer layer at 750?,a 6 nm MnxGe1-xlayer is deposited and annealed at 350 ?,and so that a quantum dot sample with high density and uniformity of size can be obtained.2.Based on the results of the orthogonal experiment.MnxGe1-x/Si quantum dots with Mn dopant leves x of 0.000.,0.032,0.046.0.058.0.068 and 0.075 were successfully prepared by changing the doping concentration of Mn.The results show that the incorporation of Mn causes the density and size of Ge quantum dots to exhibit large fluctuations.Which showed that at low Mn doping concentration,the size of the Ge island exhibits an uneven distribution,and it appears as an early stage of the Ostwald ripening stage in which the size of the quantum dots increases sharply and the density decreases sharply.When the concentration of the Mn dopant is higher than 0.058,the quantum dots exhibit a high density,small-sized film-like growth.Further characterization by Raman spectroscopy indicated that the Ge film was quite sensitive to the incorporation of Mn.which showed that the crystallinity of Ge increased with the increase of Mn dopant concentration.However,in the quantum dots of Mn dopants of 0.068 and 0.075,the appearance of the Ge-Si intermixing peak also indicates that the high Mn dopant concentration exacerbates the intermixing of the Si-Mn-Ge system.Characterization analysis of XPS found that in Mn0.075Ge0.025 quantum dot samples with Mn dopant concentration of 0.075,there may be a reaction between Mn and Ge in higher valence state,which induces the shift of binding energy in Ge and Mn atoms.The above indicates that a second phase(Mn-Ge)structure may be present in the high Mn doped Mn0.075Ge0.925 quantum dots.3.Magnetic properties studies have shown that the ferromagnetic transition Curie temperature Tc of two quantum dot samples with Mn dopants of 0.068 and 0.075 has exceeded room temperature.The doping amount of Mn is 0.032(Mn0.032Ge0.968 QDs),0.046(Mn0.046Ge0.954 QDs),0.058(Mn0.058Ge0.942 QDs),0.068(Mn0.068Ge0.932 QDs)and The Curie temperatures of the MnxGe1-x/Si quantum dots of 0.075(Mn0.075Ge0.925 QDs)are 256,277.299,321 and 310 K,respectively.Among them,an intermetallic precipitation phase(Mn-Ge)structure may be formed in Mn0.075Ge0.925 QDs.