S-Parameter and Positron Lifetime Studies of Mn Doped Zn1-Xox

Abstract

Zinc Oxide (ZnO) is an fascinating material and have potential applications as a transparent conductive electrodes for solar cells, light emmitting diodes as well as for gas sensors. Interaction between dopant, impurities and intrinsic defects plays an essential role to enhance the electrical and optical properties of ZnO thin films. Positron annihilation spectroscopy (PAS) is a non destructive technique to study thin films and nanocrystalline materials. The mechanism of positron annihilation in oxide thin films has been discussed in terms of diffusion of positrons inside the grain boundaries, nanovoids and thermally generated vacancies. The mean positron lifetime and S-parameter as a function of grain size in pure and Mn doped ZnO thin films has been calculated by using positron diffusion model. The samples are prepared by Spray pyrolysis method and temperature dependent measurements revels information about the presence of shallow positron traps like grain boundaries and interfacial defects. The calculations of shows that mean positron lifetime decreases as the grain grows. While the S-parameter increases with the increase in the siza of grains. This increase in  has been ascribed to the increase in the number of thermally generated vacancies at higher temperatures. diffusion can also be closely linked with thermal defect formation at higher temperatures. Thus, information regarding grain boundaries in thin films and nano composites can be gathered by DTM (diffusion Trapping Model). I. INTRODUCTIONPositron annihilation lifetime spectroscopy (PALS) serves as a unique tool for the characterization of lattice defects in materials science. While the annihilation lifetime yields characteristic information about the size of open-volume defects ranging from single atomic vacancies up to nanovoids, the kinematical Doppler-broadening of annihilation radiation tells about the local electron momentum distribution at the annihilation site. Annihilation lifetimes are monotonously related to the void size with a surprisingly low dependence on the material surrounding the void [1]. The semiconducting nanocrystalline thin films have great applications in electronic industry, solar cells, solar energy storage and biomedical industries. Among the nanocrystalline semiconducting materials the preparation and characterization of doped and undoped ZnO films has assumed much importance during recent years. ZnO is an important wide band gap semiconductor having wide applications in various fields such as transducers, gas sensors, transport conduction electrodes and surface acoustic wave devices etc. [2][3][4]. Zinc oxide (ZnO) is a material with great potential for a variety of practical applications due to the unique physical and chemical properties such as wide and di-rect energy band gap (~3.37 eV), large exciton binding energy (~60 meV), high electron mobility, high thermal conductivity, high radiation damage resistance and biocompatibility. The recent progress in nanoscaling of ZnO structures attracts also attention t...