Title: PREPARATION AND CHARACTERIZATION OF SEMICONDUCTOR TERNARY THIN FILMS OF ZnO GROWN BY ELECTRODEPOSITION 
Author: Mª Dolores Tortosa Jorques
Tutors: Bernabé Marí Soucase, Miguel Alfonso Mollar García
Universitat Politècnica de València
Department: Física Aplicada


ABSTRACT
   
    The main aim of the present thesis is the synthesis of ternary materials based in zinc oxide (ZnO), through the electrodeposition technique. The ternary compounds, Zn1-xCdxO, Zn1-xCoxO and Zn1-xMnxO, have been synthesized for the first time, deposited as thin films with this electrochemical process. These obtained materials show interesting optoelectronic, photovoltaic and magnetic applications. 
   The electrodeposition process has been performed in a three electrode electrochemical cell. The dymethilsulfoxide (DMSO) have been used as solvent in a solution of KClO4 0.1 M forming the electrolyte. The best conditions to obtain the materials are defined from a voltametry and correspond to 90ºC of temperature and a potential of -0.9V. The solution precursors are ZnCl2, CdCl2, CoCl2 and MnCl2 dissolved in saturated oxygen. 
      The deposited materials have been studied by diverse techniques of characterization: 
* The X-Ray Difracction (XRD) and the Raman Dispersion Espectroscopy to evaluate the crystalline structure and the deposited samples quality.
* The Dispersive Energy Espectroscopy (EDS) to identify the chemical composition of the films. 
* The Scan Electronic Microscopy to study the morphology.
* The Atomic Force Microscopy to study the surface characteristics.

   In addition, different measures to characterize optical and magnetic properties have been obtained:

* The transmittance to study the optical properties.
* The magnetic susceptibility to study the magnetic response of the materials.

   The different results show the synthesis of thin films of Zn1-xCdxO, Zn1-xCoxO y Zn1-xMnxO. Depending of the second metal concentration (Cd, Co, Mn) the crystalline structure presents variations.
   For the three compounds, when the ion concentrations of Cd+2, Co+2 y Mn+2 are low, the wurtzite structure of ZnO is maintained in the films and the Zn+2 ions are substituted by the metal ions in the ZnO lattice. The main growth direction is (002) although the lattice has been deformed. This wurtzite structure is remained until concentrations of 30% for Cd in Zn1-xCdxO (x=0.30), compared with a 20% for Co in the Zn1-xCoxO (x=0.2) and 10% for Mn in Zn1-xMnxO (x=0.1) defined these values as saturation limits for the lattice in each compounds.
   Higher concentrations of the metals in the films, form espinela structures in the compounds Zn1-xCoxO y Zn1-xMnxO which correspond to the ZnCo2O4 y ZnMn2O4  espinelas, respectively. 
   In the case of the ZnCdO films, higher concentrations of Cd in the initial solution (a 1:40 ratio related to Zn concentration) origin a crystal cubic structures of cadmium oxide (CdO).
   The growth speed depends on the different material deposited, it vary between 41nm/min for Zn1-xCoxO and 45nm/min for Zn1-xCdxO films.
   In the optical study, the transmittance is very high for the three materials, around 90% and all of them show an absorption edge in the visible range similar to the ZnO absorption edge. The introduction of Cd+2 atoms in the ZnO lattice produce a reduction of the gap energy. 
   The Zn1-xCoxO y Zn1-xMnxO films, produce a gap deformation shifting the absorption edge to the red.
   The annealing treatment effected to the films, shows an improvement in the crystalinity and adds a gap shift for temperatures not higher than 300ºC in the case of ZnCdO.
   
   For the ZnCoO y el ZnMnO samples, the annealing treatment does not produce considerable variations in the compound quality or other properties.
   Finally, the magnetic study of the ZnCoO and ZnMnO compounds, reveals a paramagnetic and ferrimagnetic behavior, respectively.
      The results obtained stand out the reliability and efficiency of the electrodeposition technique. This work shows this method as a simple process to prepare thin films of ternary compounds based in ZnO for the first time, performing the materials at low temperatures (<100ºC) with this economical and reproducible technique to deposit thin films of transparent materials with a high quality.