Effect of the base pressure achieved prior deposition on the main properties of ZnO:Al films obtained by DC magnetron sputtering at room temperature for electrical contact use

Abstract

The effect that the base pressure achieved prior to deposition has upon the electrical, optical, structural, and chemical properties of ZnO:Al (aluminum-zinc oxide, AZO) thin films was studied. The thin films were obtained at room temperature on glass substrates by direct-current (DC) magnetron sputtering with a power of 120 W (corresponding to a power density of 2.63 W/cm 2 ) and a total deposition pressure of 4.0 mTorr (0.53 Pa) with only argon gas. It was observed that all AZO characteristics and properties varied with base pressure without following a simple tendency, although some correlation was found between the crystallinity and deposition rate, with the latter depending directly upon the achieved base pressure. However, three distinct vacuum zones were identified, each of which produced AZO thin films that exhibited similar characteristics and properties.Among the base pressures studied, the lower base pressure zone [best vacuum level: under ~5.7×10 -7 Torr (~7.6×10 -5 Pa); dark yellow zone] produced dark yellow AZO thin films with moderate transmittance, but the highest resistivity and the worst stability to the environment. The middle base pressure zone [~5.7×10 -7 Torr (~7.6×10 -5 Pa) to ~7.3×10 -2 7 Torr (~9.7×10 -5 Pa); opaque zone] produced dark gray or brown AZO thin films with good conductivity, but that exhibited the worst transmittance. The higher base pressure zone [bad vacuum level: higher than ~7.3×10 -7 Torr (~9.7×10 -5 Pa); transparent zone] produced highly transparent AZO thin films with moderate resistivity. The best AZO thin film was deposited after achieving this transparent base pressure zone, but specifically in the transparent-opaque border [~7.35×10 -7 Torr (~9.80×10 -5 Pa)]. It was found that the films deposited near this transparent-opaque border within a wide margin in the direction of the transparent zone (to higher base pressure) exhibited the best transmittance, conductivity, and stability to the environment. The use of this moderate vacuum level is therefore recommended for the deposition of AZO thin films.

Modulation of argon pressure as an option to control transmittance and resistivity of ZnO:Al films deposited by DC magnetron sputtering: on the dark yellow films at 10-7 Torr base pressures

“…Also, the inverse relationship between crystallinity and deposition rate was confirmed, in which deposition rate inversely depends on argon pressure. The overall results presented in this paper complement our previous work about the effect of base pressure on properties of AZO thin films [10], and therefore the reader is referred to such a work for more details.…”

“…Variation tendency of the (a) integrated percent transmittance and resistivity, and (b) peak intensity of the (002) plane and deposition rate of the AZO thin films as functions of the base pressure achieved before the sputtering-deposition. See our previous work about the effect of base pressure [10]. FIGURE 2.…”

“…The base pressure achieved prior to the sputtering deposition of a given material is an important parameter that strongly influences its final characteristics and properties [1][2][3][4]. The different vacuum levels achieved before the deposition process is especially important for transparent conductive oxides (TCOs) [5][6][7][8][9][10], where it is necessary a high transparency to the solar radiation (particularly to the radiation of interest for the device) and a very good conductivity to act as a front electrical contact for application in solar cells [11]. In this context, in a previous work [10] we studied the effect of the vari- The variation tendency of the relevant parameters studied in such a research is summarized in Fig.…”

“…The different vacuum levels achieved before the deposition process is especially important for transparent conductive oxides (TCOs) [5][6][7][8][9][10], where it is necessary a high transparency to the solar radiation (particularly to the radiation of interest for the device) and a very good conductivity to act as a front electrical contact for application in solar cells [11]. In this context, in a previous work [10] we studied the effect of the vari- The variation tendency of the relevant parameters studied in such a research is summarized in Fig. 1, which was divided into color zones according to the approximate appearance of the corresponding produced AZO thin films.…”

“…Although the background looks gray to the eye owing to the digitalization of the figure, it constitutes a reference for comparison: the AZO films deposited at higher base pressure (right) show a color similar to the background, indicating its high transparency. For more details, see our previous work about the effect of base pressure [10].…”