Long-Term Stability of Epitaxial (Nd1–xGdx)2O3 Thin Films Grown on Si(001) for Future CMOS Devices

The (Nd
_1–x
Gd
_x
)
₂
O
₃
thin films were grown on Si(001) in 2005 using molecular beam epitaxy followed by an in vacuo metallization of Pt contacts. Pt/(Nd
_1–x
Gd
_x
)
₂
O
₃
/Si(001) metal-oxide-semiconductor structures have been characterized several times over the period of 2005–2015 in order to investigate the stability of their physical and electrical properties. Core-level X-ray photoelectron spectroscopy (XPS) spectra remeasured during 2015 depict that the layer still retains its original properties that were measured in 2005. Although there has been some degradation of electrical properties such as capacitance and leakage current over several years, interestingly the midgap density of interface traps’ (
$D_{{\mathrm{it}}})$
value has been found to be decreased from
$1.1 \times 10^{12}$
to
$3.5 \times 10^{11}$
eV
$^{-1}$
cm
$^{-2} $
over the years. The formation of silicate-like interface inferred from XPS measurements can be attributed to such an improvement over this period. Time-dependent dielectric breakdown measurements under constant current stress and constant voltage stress were also carried out to investigate the reliability of the structure.