Investigation of structural properties of transparent conductive oxides

Transparent conductive oxide (TCO) films are photovoltaic materials which have high electrical conductivity and optical transmission features. Because of these properties, they are used in solar cells as front surface electrode and also in low-emission glasses and touch-operated applications. So far in commercial applications three types of transparent conductive oxide films are used which are Tin-Oxide (SnO2), Indium-Tin-Oxide (ITO) and Zinc-Oxide (ZnO). Aluminum, gallium, magnesium, indium are added as the doping elements to the Zinc-Oxide films. Electrical properties are improved by increasing carrier mobility in the structure with this addition of elements. Some post deposition techniques are used to the transparent conductive oxide films to improve optical, electrical and surface properties. The main ones of these techniques are annealing and surface etching. Post annealing change grain size and composition of the structure, thus optical and electrical properties of the film is improved. Films that are not at the desired values of surface roughness after the deposition are applied surface etching to improve to increase light trapping features. After deposition of transparent conductive oxide film in the present study examined the effect of the process. Processes of determining the effects of post-annealing on electrical, structural and optical features were performed in different durations and temperatures in atmosphere with the help of hot plate. Experiments carried out at 100 °C, 200 °C and 300 °C for each temperature value at 15 minutes, 30 minutes, 45 minutes and 60 minutes of durations. In order to examine the effect of surface etching; GZO films immerged into 0.1% of HCl solution for performing the chemical etching process at 1 second, 2 seconds, 3 seconds, 4 seconds and 5 seconds of periods. Wide variety of techniques used in characterization of grown thin films. Film thicknesses were measured by the method of scanning electron microscope (SEM). Resistivity values of films were calculated with four-point probe. Optical transmittance values have been measured with optical transmittance (UV-VIS). Surface roughness values were determined with atomic force microscope (AFM). To determine the efficiency criteria in the transparent conductive oxide layers, conductivity and optical absorption rate which is also called as "figure of merit" was calculated with each other. As a result of the post-annealing experiments resistivity values of only ZnO films are reached to >10-2 Ω.cm, optical transmission values were calculated > 83% amounts. Band gap decreased to 3.30 eV from 3.40 eV, FOM values increased at the end of 15th and 30th minutes at 200 °C. Resistivity values of AZO films are reached to maximum >10-2 Ω.cm and optical transmission values were calculated > 87% amounts after the heat treatment processes. Band gap values decreased to 3.71 eV from 3.98 and FOM values have undergone a decrease of 40%. Electrical resistivity values of GZO films generally have not overcome the >10-3 Ω.cm level, optical transmission values were measured at 81% amounts. Band gap decreased to 3.80 eV from 4.00 eV, FOM values decreased maximum 31% rate. Resistivity values of GZO films which were performed surface etching increased almost 2 times to 2.2461x10-3 from 1.222x10-3 after the 5th second. Optical transmission values of the films were changed 84-85% rate. Band gap values have undergone a decrease to 3.85 eV from 4.00 eV values. FOM values decrease 50% rate at the end of the 5 seconds and surface roughness amounts increased approximate 2 times to 9.35 nm from 5.10 nm.