Electrical properties of amorphous carbon films

Abstract

Aromatic polyimide films, Upilex S partially carbonized between 700°C and 1000°C. Electrical conductivity is higher at higher temperatures. The electrical conductivity s could be expresses as s = so exp (−E/kT), where k is the Boltzmann constant, t is the absolute measuring temperature. so and E are found to be 4 × 10−1 Ω−1 m−1 and 0.02eB, respectively. The experimental data show that the Hall coefficient R is negative, and this implies that the carriers are negatively charged, i.e. electrons. The specimens are n-type semiconductors. The carrier density η is given by η = 1/(|e|R) and the mobility μ is μ is s/(η|e|), where |e| is the absolute value of the electron charge and s is the electrical conductivity. Fitting the data, η = A1 exp (−E1/κT) and μ = A2 exp (E2/κT). E1 and E2 depend on carbonized temperature. The polyimide films are not completely carbonized but partially carbonized at 700°C. The partially carbonized polyimide is an n type donor. It is concluded that the “impurity level” lies about 0.36eV below the conduction band.