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