Temperature dependent transport properties in molybdenum oxide doped α-NPD

The temperature dependent transport properties of molybdenum oxide (MoO3) doped N,N'-di(1-naphthyl)-N,N'-diphenylbenzidin (α-NPD) were studied over a frequency range of 100 Hz to 1 MHz. The value of trap density and mobility calculated by detailed analysis of current-voltage (I-V) characteristics are 9.43 x 1026 m-3 and 1.23 x 10-6 cm2 V-1 s-1, respectively. The relaxation time for the carriers in the bulk and in the interface region decreases with temperature. The Cole-Cole plot indicates the device can be modeled as the combination of two parallel resistor-capacitor (R-C) circuits with a series resistance of around 70 Ω. The dc conductivity shows two different regions in the studied temperature range with activation energy of Ea ∼ 0.107 eV (region I) and Ea ∼ 52 meV (region II), respectively. The ac conductivity follows the universal power law and the onset frequency increases with increase of temperature. The temperature dependent conduction mechanism can be explained by correlated hopping barrier (CBH) model.