Figure 7 Annealing temperature dependences of sheet resistance, carrier concentration and Hall mobility of the IHfO:H films prepared with 0.8 % H2 concentration.
As can be seen from Figure 7, the Hall mobility of the IHfO:H films increases rapidly from the as-deposited 41.48 cm2V-1s-1 to 102.92 cm2V-1s-1with an annealing temperature of 200 °C. However, as the annealing temperature is keep increasing to 250 °C, the Hall mobility decreases. The annealing temperature dependence of mobility seems to be consistent with that of the crystallinity, as shown in Figure 6, which implies the possible relationship between the rise of the mobility and the reduced grain boundary scattering.29 However, the carrier concentration does not increase with the annealing temperature, but shows an opposite tendency as depicted in Figure 7, although it is generally believed that crystallization could promote the activation of dopants.35 The significant decrease of carrier concentration with annealing temperature, which actually determines the change of sheet resistance, represents the reduced concentration of doping impurity. The weakened ionized impurity scattering and the improved crystallinity together lead to the improvement of the mobility of the IHfO:H films. The slight decrease of the mobility and the average grain size at the annealing temperature of 250 °C are probably related to the escaping of the hydrogen. 34,35