Electrical properties of amorphous carbon films

Aromatic polyimide films, Upilex S partially carbonized between 700 degrees C and 1000 degreesC. Electrical conductivity is higher at higher temperatur es. The electrical conductivity s could be expresses as s = s(o) exp (-E/kT ), where k is the Boltzmann constant, t is the absolute measuring temperatu re. s(o) and E are found to be 4 x 10(-1) Omega (-1) m(-1) and 0.02eB, resp ectively. The experimental data show that the Hall coefficient R is negativ e, and this implies that the carriers are negatively charged, i.e. electron s. The specimens are n-type semiconductors. The carrier density eta is give n by eta = 1/(/e/R) and the mobility mu is mu is s/(eta /e/), where /e/ is the absolute value of the electron charge and s is the electrical conductiv ity. Fitting the data, eta = A(1) exp (-E-1/kappaT) and mu = A(2) exp (E-2/ kappaT). E-1 and E-2 depend on carbonized temperature. The polyimide films are not completely carbonized but partially carbonized at 700 degreesC. The partially carbonized polyimide is an n type donor. It is concluded that th e "impurity level" lies about 0.36eV below the conduction band. (C) 2001 Ac ta Materiallia Inc. Published by Elsevier Science Ltd. All rights reserved.