Influence of temperature and frequency on electrical properties of electron beam evaporated bromoaluminum phthalocyanine, BrAlPc, thin films

Abstract

The AC electrical properties of electron beam evaporated Bromoaluminum phthalocyanine (BrAlPc) thin films have been studied in the frequency range 10²–10⁵ Hz and in the temperature range of 303–413 K. The BrAlPc thin films are characterized by field emission scanning electron microscopy (FESEM). The capacitance is found to be sensitive to the frequency and increases with increasing temperature and decreases with increasing frequency. A loss minimum has been observed in the frequency dependence of the dissipation factor. Such behavior is found to be in good qualitative agreement with the model of Goswami and Goswami. The AC conductivity $\sigma \left( \omega \right)$ is found to vary as $\omega^{s}$ in the studied frequency range. At frequencies 10–10² Hz, s is less than unity and decreases with increase in temperature indicating a dominant hopping process. At frequency ranges 10²–10⁴ Hz, exponent s lies very close to the unity and is independent of temperature, which shows the quantum mechanical tunneling is dominated conduction mechanism. At higher frequencies 10⁴–10⁵ Hz, s is found to be temperature independent. The temperature dependence of AC conductivity shows a linear increase with the increase in temperature. Moreover, the activation energies of device are determined as a function of frequency.