Positive temperature coefficient of resistance of Mg-GeO2 nanowire array film

Abstract

Here, glancing angle deposition is employed to synthesize the undoped GeO2 and Mg-doped (0.4 and 0.8 at. %) GeO2 nanowires (NWs) on a Si substrate. The microscopic images show the formation of the NW-like morphology of the grown materials. The gradual decrease in the average ratio of length to diameter depicts the worsening of the formation of NWs with the incorporation of Mg into the GeO2 host lattice. This also affects the crystallinity characteristics of the materials, which have been demonstrated from the selected area electron diffraction (SAED) pattern of the materials. The polycrystallinity nature of undoped GeO2 NWs changes to amorphous due to the introduction of Mg, which has been confirmed from both the obtained SAED and x-ray diffraction patterns of the samples. The presence of Mg was confirmed from the obtained broad bands at 473 and 437 cm−1 in the Fourier transmission spectrum of the doped samples. The increasing conductance with the temperature of Au/undoped GeO2 devices can be explained by the thermionic emission process, whereas the Mg-GeO2 device shows an overall decrease in conductance with increasing temperature. We have ascribed the origin of this abnormal conductance as the positive temperature coefficient of resistance, which is one of the first reports, due to the generation of random grain boundaries and enormous electron trapping at the Au/Mg-GeO2 NW junction. Furthermore, the undoped GeO2 NW device shows good temperature-dependent conductivity as well as stability compared to the doped one.