CHARGE TRANSPORT AND GAZ SENSING PECULIARITIES OF NANOCRYSTALLINE AND AMORPHOUS TELLURIUM FILMS

Abstract

Nanocrystalline and amorphous tellurium thin films have been prepared and their both DC and AC electrical conductivity was investigated to receive the information concerning mechanisms of charge transport at different temperatures, environments and frequencies of the applied electrical field. SEM and XRD analysis have been used for structural investigation of the films but the impedance spectroscopy was applied for the transport mechanisms determination. Effect of the environment was studied by application of small concentrations of nitrogen dioxide, paying attention to both times and magnitude of response, followed by recovery of origin state after the target gas is removed. It is shown that the nanocrystalline structure of the film can be transformed into an amorphous one through growth rate increase. Such transformation however, does not affect the mechanism of charge transport up to frequencies of 105 Hz, which is due to electrical charge carriers excited above mobility band gap edges. At higher frequencies, the AC conductivity of amorphous films strongly increases with frequency increase, which is explained by transition to another transport mechanism that includes the charge carriers hopping via localized states in the gap. Both nanocrystalline and amorphous films react with nitrogen dioxide diluted in an air environment but their gas - sensing parameters differ. Results are explained in terms of interaction between gas molecules and lone – pair electrons of tellurium atoms influenced by roughness (compactness) of the films disturbed at disordering (amorphisation) increase.