The ZnO thin films were deposited using a route based on the
plasma assisted reactive evaporation method, which consists
of evaporating Zn in the presence of oxygen, so that there
takes place a chemical reaction that gives place to the formation
of the ZnO. As the Zn in the presence of O2 oxidize very
slowly at room temperature, it is necessary to ionize both Zn
and O2 to accelerate the chemical reaction between these two
species. The ionization is achieved through GD that includes
different ionized species that increase the speed of chemical
reaction and therefore the rate of growth of ZnO film. Under
the conditions of current and pressure used in the reactive
evaporation process, the generated plasma is a non-thermal
plasma that implies that the most probable mechanism of
ionization of the gas inside the plasma is direct ionization
of neutral particles (atoms, molecules or radical) by electron
impact [23].
For the design of the reactor that allows generating a stable
GD confined in the space between the electrodes, it took into
account the Paschen law that relates the voltage for the initiation
of the discharge and the product of the pressure by the
separation distance between the electrodes [23]. For the reactor
designed in this work and under the conditions of pressure
used, it was found that for oxygen, a stable glow discharge
is obtained by applying a voltage difference of the order of
500 V.
Fig. 1 shows a scheme of the setup designed and implemented
to grow ZnO thin films by plasma assisted reactive
evaporation. This includes the following units: