Figure 4 The decomposed O 1s XPS lines of the IHfO:H films deposited
with different H2 concentrations of (a) 0 %, (b) 0.5
%, (c) 0.8 %, (d) 1.2 %, and (e) 1.5 %. All the IHfO:H films were
annealed at 200 °C.
Figure 4 illustrates the O 1s core level peaks of the XPS spectra for
the IHfO:H films deposited with different hydrogen concentrations. The O
1s XPS lines can be decomposed to three peaks of OA,
OB, and OC, with the corresponding
binding energies of ~530.0 eV, ~531.1
eV, and ~532.1 eV, respectively. The OApeak with the lowest binding energy of ~530.0 eV
corresponds to the O2- ions in the
In2O3 lattice. The OBpeak at ~531.1 eV corresponds to the oxygen vacancy Vo.
The tiny OC peak at ~532.1 eV can be
attributed to the hydroxyl bonds appearing in In(OH)3 or
InOOH.27
It can be seen that, the content of oxygen vacancies (OBpeak) in different IHfO:H films shows a slightly decrease as the
H2 concentration increasing from 0 % to 0.8 % and then
a rapid increase when the H2 concentration rises from
1.2 % to 1.5 %. The trend of the oxygen vacancy content varied with
the H2 concentrations is similar to that of the carrier
concentration as shown in Figure 3, which demonstrates the influence of
H doping on the oxygen vacancy content and thus the carrier
concentration. However, a less than 5 % change in oxygen vacancy does
not seem to be sufficient to explain the more than 60 % increase in
carrier concentration as the hydrogen concentration rises from 1.2 % to
1.5 %. The contribution of hydrogen as a donor to the carrier
concentration should also be considered. As mentioned above, hydrogen in
TCO films exists in the forms of Hi+and Ho+. The amount of the
interstitial hydrogen Hi+ can be
equated with the amount of hydroxyl (OCpeak)31 which exhibits an increase with increasing the
hydrogen concentration as observed by Huang et al.27The sharp rise in the carrier concentration can also be attributed to
the sudden rise in the interstitial hydrogen content. In addition, the
substitutional hydrogen from the excess hydrogen doping during the
deposition would also cause an increase in the carrier
concentration.31