Investigation of nanostructured Pd–Ag/n-ZnO thin film based Schottky junction for methane sensing

Abstract

Undoped nanocrystalline n-type ZnO thin film was deposited by chemical deposition technique on a thermally oxidized p-Si (*5 X cm resistivity and \100[ orientation) substrate. Formation of stable zinc oxide thin film was confirmed by two-dimensional X-Ray Diffraction (XRD) and EDX analysis. The average crystallite size of the ZnO sample was evaluated as *50 nm. The surface was characterized by Field Emission Scanning Electron Microscopy (FESEM) and Atomic Force Microscopy (AFM) that confirm the formation of nanocrystalline (grain size *50 nm) ZnO thin film with surface roughness of *100 nm. Good conversion of precursor into ZnO thin film in the chemical deposition method was evident by Fourier Transform Infrared Spectroscopy (FTIR). A small peak at 479 cm-1 was observed in the FTIR spectrum confirming the formation of quartzite structure of the ZnO. The band gap (*3.44 eV) of the material was calculated from the optical absorption spectroscopy. To prepare Pd-Ag/n-ZnO Schottky junction, Pd-Ag contacts were taken by electron beam evaporation method. I-V characteristics of the junction were studied at different temperatures in inert and reducing ambient (N 2 and N 2 ? CH 4) with turn on voltage of around 0.2 V. The parameters like ideality factor (g), saturation current (I 0), series resistance (Rs), and barrier height (U BO) of the junction were calculated in the temperature range 50-200°C in N 2 as well as in 1 % CH 4 ? N 2 ambient. It was observed that the ideality factor decreases in the temperature range 50-200°C (g = 12.34 at 50°C and g = 1.52 at 200°C) in N 2 ambient and g = 1.18 in N 2 ?CH 4 ambient at 200°C. Schottky Barrier Height (U BO) of the Pd-Ag/n-ZnO junction was found to increase with temperature. A close observation of Pd-Ag/ n-ZnO junction in the presence of methane was performed to appreciate its application as methane sensor. The sensing mechanism was illustrated by a simplified energy band diagram.

Experimental and theoretical investigations on temperature and voltage dependence of an Au/AZO thin-film Schottky diode

“…XRD pattern of AZO on glass substrates show three weak peaks appearing at 31.7, 34.0, and 36.0° related to (100), (002) and (101) planes, respectively, of ZnO in its hexagonal structure with a little shift to lower degrees which can be assigned to Al in this structure according to the JPDS card No. [0075-080-01] [9,10], which indicates the existence of aluminum in the segregation boundaries and increase of the oxygen capture content by the Al 3+ ions compared to Zn 2+ with a larger atomic charge, and the tension or strain resulting from it will cause the (002) plane to move toward the lower degrees [14]. To calculate the average size of the crystalline domains of deposited films, we used the Debye-Scherrer equation as follows [15,16]:…”

“…Their structural, electrical, and morphological properties have been characterized and we have also determined the Cu 2 O/AZO heterojunction diode properties [4]. The result showed a low turn-on voltage of about 0.64 V, which indicates that the heterojunction acts as a rectifier diode [9]. Thus, the result of experiment and theory is quantitatively compared at high temperature because the voltage of the film is measured at 10 V. We obtain good agreement between the experiment and theory for the temperature-dependent resistivity of the film.…”

“…The result showed the amorphous behavior in which its structure has been modified to crystalline post-annealing. In another work, Roy et al [9] deposited n-type ZnO on a Si substrate by chemical deposition technique by which the average crystallite size of the film was evaluated to be about 50 nm. They also obtained an optical bandgap of about 3.44 eV using the optical absorption spectroscopy.…”

Nanoflower ZnO thin-film grown by hydrothermal technique based Schottky diode

“…ZnO is an attractive compound for solid state semiconductor devices because of its electronic, piezoelectric and optical characteristics. This material is easy to synthesize, environmentally friendly, cost-effective, and has high exciton binding energy and self-assembly of different nanostructure size and shapes [5][6][7][8] . ZnO nanostructures include nanoparticles, nanorods, nanowire, nanorings, nanoflakes, nanocombs, nanoflowers, nanosprings and nanobelts [8,9] .…”