Abstract:
Zinc Oxide (ZnO) is one of the most important candidates for a II-VI room-temperature
diluted magnetic semiconductor (DMS) by doping with a transition metal. ZnO based
DMSs are particularly attractive as candidates for integrating optical and electronic
properties into a single substance. ZnO and copper (Cu) doped ZnO thin films were
synthesized from the precursors Zn(CH3COO)2.2H2O and Cu(CH3COO)2.H2O by using
a “Spray Pyrolysis Deposition” technique at 623K substrate temperature containing 0, 5,
9, 15, 20 and 25 at% Cu concentrations. The surface morphological, structural,
electrical and optical properties of the as-deposited ZnO films have been investigated as
a function of Cu-doping level. The thickness of the films was estimated by Fizeau
fringes interference method which varied from 195 to 198 nm.
The scanning electron microscopy (SEM) micrographs of as-deposited films shows that
all the films are found well covered on the glass substrate. Nanofibers are observed
around the nucleation center in pure ZnO thin film. Due to interstitial holes of ZnO are
filled with copper, the fiber has broken and transform into grain. The size of the grain
decreases with the increase of Cu concentration. Energy Dispersive Analysis of X-ray
(EDAX) results clearly showed that the grains are typically comprised of both Zn and
O for pure and Zn, O, and Cu for Cu doped films. From EDAX data it is found that
atomic weight % of Cu is increased with the increase of Cu concentration in Cu doped
ZnO films.
X-ray diffraction studies showed the amorphous polycrystalline nature of the films with
preferential orientation along the (100), (002), (101), (102), (110), (103) and (112)
planes. Structure of the material has been identified as hexagonal wurtzite. The peaks
are found to shift from their standard positions in the presence of the Cu dopant due to
the positioning of dopant atoms into interstitial lattice sites.
Various optical constants such as absorbance, transmittance, refractive index and
dielectric constant of the films have been studied for the as-deposited films are
recorded in the wavelength ranges from 300 to 1100 nm. For as-deposited Zn1-xCuxO
films, the band gap varies from 3.21 to 3.05 eV as Cu increases. The resistivity
gradually decreases with the increase of temperature, which indicates the semiconducting
nature of the materials. The activation energy is increasing up to 9% and then it
decreases with the higher percentage of copper concentration.
