C - V characteristics of MOS capacitors for different material
Yes. You are correct, if they all have the same cros sectional area and same doping concentration in the semiconductor. 

For a MOS capacitor, the capacitance value in inversion region is given by the the series combination of insulator capacitance (\$C_{ox}\$) and the semiconductor capacitance in inversion (\$C_{s}\$). Since all the three capacitors have same capacitance in the accumulation region, \$C_{ox}\$ values are same. \$C_s\$ depends on dielectric constant of the semiconductor (\$\epsilon_s\$) and doping in the material. So if the doping is can be assumed to be same, then MOS capacitor with least \$C_s\$ will have lowest capacitance.