Electron transport and sensor characteristics of tin dioxide based nanocrystalline materials.

摘要

Wide band gap, transparent semiconductor SnO2 is an n-type conductor and is widely used as a sensor material as well as transparent electrode material e.g. in solar cells and flat panel displays. Recent discovery of p-type doping with Li has opened exciting possibilities in new classes of sensors and transparent nanoelectronic devices. Li-doping in SnO2 nanoparticles was explored through a gel-sol method of synthesis to examine the influence of reaction conditions such as pH, dopant concentration, and calcination temperature. The Li doping in nanoparticles was characterized using nuclear reaction analysis and the nanostructure with high-resolution electron transmission microscopy and X-ray diffraction techniques.;Direct current conductivity of the nanocrystals was investigated from 25 to 350°C. Efros-Shklovskii Variable Range Hopping (ES-VRH) conduction mechanism was observed at temperatures below 100°C with a cross over to 2D-Mott Variable Range Hopping (M-VRH) conduction at temperatures above 250°C. Thick film conductive Cl2 sensors were fabricated using nanoparticulate SnO2 doped with Sb. The fabricated sensors were tested against gases like Cl2, Br2, HCl, NO, NO2, CHCl 3, NH3 and H2. The highest response to Cl 2 was achieved in 0.1% Sb doping where an exposure to 3ppm of Cl 2 gas led to 500 fold increase in device resistance. The high sensitivity to Cl2 was accompanied by minor interference due to other gases at room temperature. It was found that the SnO2 doped with 0.1% Sb exhibited high response, selectivity (>100 in comparison to the gases described above) and short response time (∼60s) to Cl2 at 3 ppm level at room temperature.;Using a compression technique, porous diodes consisting of n-type (antimony doped) and p-type (lithium doped) SnO2 nano-particulate films were prepared. Typical current-voltage curves of such devices resembled the behavior of a typical diode but for one key difference, owing to the porosity of the film, areas near the p-n interface and the p- and n-regions are accessible to gaseous analytes. Their sensor capabilities were measured through alternating and direct current measurements. These porous diodes were capable of detecting 400 ppb Cl2 at room temperature and had a 40s response time.