The capacitance of Schottky diodes prepared by the evaporation of Pd onto undoped and phosphorous doped a - Si : H film is studied as a function of frequency, temperature. Also the density of state distribution of undoped sample is determined from $C^2(dC/dT)^{-1}$ versus temperature plots.
By this plots, the density of state distribution of undoped samples is smaller than that by Field Effect experiment and the density of state near Fermi level is $- 10^{16}ev^{-1} cm^{-3}$.
In case of a doped sample, the determination of density of state near Fermi level is difficult because of thin depletion layer width.
