Study of morphological and electrical properties of the ZnO/p-Si hetero-junction: Application to sensing efficiency of low concentration of ethanol vapor at room temperature

In this work, thin films of ZnO were deposited by DC reactive sputtering of zinc target under (Ar and O-2) gas atmosphere, at a deposition temperature of 100 degrees C. A series of samples were prepared on both corning glass and p-doped crystalline silicon substrates, at different Ar flow rates (F-Ar) ranging from 0.5 and 2.5 sccm. The films properties were investigated by atomic force microscopy (AFM), Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD). The results showed thin films with rough surfaces and polycrystalline structure. The electrical study (current-voltage characteristics) of ZnO/p-Si hetero-junctions revealed a rectification behavior. The highest forward current was obtained for F-Ar = 1.5sccm. The exposure at room temperature of ZnO/p-Si heterostructures to ethanol vapors showed a high gas sensing response for ZnO/p-Si hetero-junctions with rough surface and high forward current, corresponding to F-Ar = 1.5 sccm. For a low concentration of ethanol vapor (10 ppm), the dynamic response at room temperature of ZnO/p-Si hetero-junctions revealed a sensitivity ranging from 40 to 80% with response and recovery times of 5 and 3 s respectively. Comparing these characteristics to those already obtained by other teams showed that the elaborated devices in this work are good candidates for fast sensors of low concentrations of ethanol vapors at room temperature.