Anomalous electrical transport properties of CdSe quantum dots at and below room temperature

Here we report the dielectric relaxation and anomalous ac conduction behavior of CdSe quantum dots in the temperature (T) range of 77 K <= T <= 300 K and in the frequency (f) range of 100 Hz <= f <= 1 MHz. Interfacial polarization exhibits strong temperature dependence only above 250 K and dielectric loss spectrum undergoes a shallow minimum. Superlinear power law behavior of the ac conductivity was observed above certain frequencies, along with the universal dielectric response at comparatively lower frequencies. Extraction of the temperature dependent dc contribution, hopping frequencies, frequency exponents and activation energies values were done by theoretical fitting and was observed that for T=77-200 K, classical hopping over barrier (HOB) is the prevailing charge transport mechanism whereas for T=250-300 K, the charge transport mechanism is correlated barrier hopping (CBH). Analysis of the Nyquist plotting and non-Debye electric modulus spectra have also been conferred in this context. (C) 2013 Elsevier B.V. All rights reserved.