1. Strained MxSi1-x(M=Fe, Mn) layer on virtual substrate: growth, morphology
Yuanmin Shao, and Zuimin Jiang
Phys. Dept., Fudan Univ., Shanghai, People’s Republic of China
Motivation
Si-based dilute magnetic semiconductors (DMSs) are regarded as promising function materials for spintronics.
Strain could be used to ajust the distance between impurities and Si atoms in DMSs so as to change the their magnetism. Therefore, it is worth investigating the correlation among the strain, microstructures and physical properties of the films.
I. Fabrication of GexSi1-x virtual substrate
Raman spectra
Growth conditions
AFM height image
excitation wavelength: 325nm
excitation wavelength: 514nm
Si-Si (substrate)
Si-Si
Si-Si (GexSi1-x)
300nm
Ge 20%
Ge 30%
Ge-Si
Ge-Si
250nm LT-Si
Si (001)
10 μ m× 10 μm
10 μ m× 10 μm
Ge-Si
Ge-Si
Roughness: 0.67nm
RMS: 0.85nm
Roughness: 1.37nm
RMS: 1.82nm
A low temperature (LT) Si buffer layer was first grown on Si (001) substrates at 450℃ to reduce the threading dislocation density in the SiGe layer. Then a GexSi1-x films was grown on the top of the LT Si buffer at 550℃.
Smooth surfaces with no straight crosshatch lines were fabricated and we are able to keep the surface roughness of Ge0.2Si0.8 layer under 1 nm.
From the positions of Ge-Si peaks and Si-Si peaks with the 325nm radiation, the GeSi strain relaxation of the Ge0.2Si0.8 sample surface was determined to be 98%, while that of the Ge0.3Si0.7 sample was 89%.
II. Fabrication of strained MxSi1-x(M=Fe, Mn) layer on Ge0.2Si0.8 Virtual Substrate
Raman spectra
Growth conditions
Unstrained MnxSi1-x layer
FexSi1-x layer
Strained MnxSi1-x layer
strained
unstrained
Si-Si (511.9)
Si-Si (518.5)
2nm Si
2nm Si
Si-Si (520.7)
excitation wavelength: 325nm
excitation wavelength: 325nm
excitation wavelength: 325nm
10nm MxSi1-x
10nm MxSi1-x ×9 ×9
10nm Ge0.2Si0.8
10nm Si
MnSi1.73
MnSi
amorphous Si
10nm MxSi1-x
MnSi1.73
10nm MnxSi1-x
300nm
MnSi
300nm LT-Si
Si-Si (516.3)
300nm LT-Si
Si substrate
amorphous Si
Si substrate
The MnxSi1-x multilayers were grown at 200 ℃ and then in-situ annealed at 400 ℃. From the Raman spectra of as-grown sample, we find MnSi phase has formed before the crystallization of Si. With the annealing temperature rising to 600 ℃, Si was crystallized and MnSi phase changed into MnSi1.73 phase. Furthermore, even in the unstrained sample, we could still find the Si-Si peak deviating from cm-1, which suggests the Mn-Si alloys introduced tensile strain in Si.
The FexSi1-x multilayers were grown at 400 ℃. However, no Fe-Si phases were found in Fe doped Si multilayers.
On the top of Ge0.2Si0.8 virtual substrate, strained and unstrained M doped Si multilayers were grown.
III. Conclusions
Smooth GexSi1-x virtual substrates were frabricated on Si (001) substrate.
The microstructures of strained and unstrained multilayers were determined by Raman spectra. No Fe-Si alloys were found to form at the grown temperature of 400 ℃. However, in MnxSi1-x multilayers, MnSi was found to form before the crystallization of Si, which is harmful to the formation of DMSs. Furthermore, the crystallization of MnSi1.73 would introduce extra tensile strain in crystal Si.