Association

5.3. Interface engineering I: Hydrogen passivation of the EuO/Si interface 109
110
100
90
80
70
60
50
102 101 100 99 98 97
T S = 350 °C, Si
T S = 450 °C, Si
20
T S = 350 °C
pure Si
0.65 nm
silicide
T S = 450 °C
pure Si
0.30 nm
silicide
50
9.7% EuSi y
T S = 350 °C, H-Si
T S = 450 °C, H-Si
10
0
50
25
T S = 350 °C
H-Si
0.56 nm
silicide
4.4% EuSi y
T S = 450 °C
H-Si
0.14 nm
silicide
25
0
60
30
0
0
96.5
102.5 100.5 98.5
100.5 98.5 96.5
102.5
Figure 5.19.: The EuO/H-Si interface analyzed by least-squares peak fitting of the Si 2p core-levels.
the epitaxial growth mode of thin EuO films on Si, while at higher T S heteroepitaxy of EuO
directly on Si (001) is generally possible.
A chemical insight into the buried EuO/Si (001) heterointerface is obtained by a HAXPES
analysis of the Si orbitals from the interface. We select an interface-sensitive geometry by
tuning the excitation energy to a minimum of 2.3 keV together with off-normal emission. The
recorded Si 2p peaks are shown in Fig. 5.19c–d for the different interface treatments. With a
chemical shift of −0.6 eV, the silicide component can be clearly identified on the low binding
energy side of the bulk Si doublet peak. The silicide fraction shows a clear development: an
increase of substrate temperature as well as the hydrogen passivation of Si reduce the silicide
thickness.
In order to quantify the silicide reaction at the EuO/Si interface for every set of passivation
parameters, we conduct a peak fitting analysis based on the least squares method. The resulting
thicknesses of the buried interfacial silicide layer are summarized in Fig. 5.20. Comparing
the diminishments of the interfacial silicide, the impact of synthesis temperature from
350 ◦ C to an optimum of 450 ◦ C on the EuO/Si interface reaction is larger (−38% silicide)
than the application of hydrogen termination (−14% silicide) to the clean Si surface. The
advantage of a higher synthesis temperature can be understood from a thermodynamic analysis
of EuSi 2 (Ch. 5.2): this silicide favors a disappearance reaction during EuO distillation
growth (Fig. 5.10) yielding EuO and Eu. Any excess Eu, however, is readily re-evaporated at
higher T S , thus minimizing the available constituents for silicide formation. The advantage
of a hydrogen passivation, although smaller than for the temperature variation, is explained
by its larger thermodynamic stability compared to the silicide (Fig. 5.8). In conclusion, the
parameters for a minimized interfacial silicide formation (d min (EuSi 2 ) = 0.14 nm) are the ap-