Electrical and Photoelectrical Properties of ZnO Random Nanowire Network Thin Film

VEGA, NADIA CELESTE; TIRADO, MONICA CECILIA; COMEDI, DAVID MARIO

Beijin

Simposio; The 16th International Symposium on Metastable, Amorphous and Nanostructured Materials; 2009

Random nanowire networks are emerging materials with promising applications in transparent and flexible electronics for new generation photovoltaics and lighting, and for high surface area chemical sensors, among others [1]. ZnO nanowires have attracted much interest recently due to their interesting properties, such as piezoelectricity and large exciton binding energy. We have studied the electrical conductance and photoconductance of ZnO random nanowire networks as a function of temperature and applied bias voltage. The nanowire samples were grown on a SiO2 coated Si wafer in a pumped quartz tube furnace under high purity Ar flow. A crucible containing graphite and ZnO powder was placed at a position corresponding to the furnace center (1100ºC), while substrates were placed downstream the tube (500ºC- 700ºC). To promote nanowire growth, the SiO2 surface was covered with Au clusters (0.5nm thick Au layer evaporation and annealing [2]). I-V curves were recorded by coplanar metallic contacts in the 10-300K range. The conductance was measured as a function of the film temperature with a constant voltage set at value within the ohmic (linear) region. Photoconductance was measured by illuminating the film with a UV beam (300 nm). The conductance of the network increases with temperature and can be approximated by a Mott’s variable range hopping dependence in the 10-70K range. For larger temperatures a new mechanism sets in, which is characterized by a faster growth with temperature. The photoconductance shows an initial fast increase after switching on the illumination, followed by a very slow increase that does not reach steady state after several hours of illumination. The photoconductance decays non-exponentially with time after interrupting the illumination, and displays quasi-persistent behavior. The results are discussed in terms of various conduction and trapping models.