Study of annealing influence on electrical and morphological properties of ZnO:Ga thin films

Abstract

In this study, the influence of thermal annealing in different ambients on the electrical and morphological properties of Ga-doped ZnO films with 1wt.% gallium acetylacetonate in the precursor mix is investigated systematically. As-grown samples were prepared on c-plane Al 2 O 3 by PEMOCVD with a substrate temperature of 300 o C and possess a resistivity of about 10 -2 Ω·cm. The annealing was realized in isochronal steps between 300 to 1000 o C for 1 hour in argon and air ambient, respectively. The resistivity of the films was found to be dependent on the annealing atmosphere. During annealing in air, the resisitivity increases monotically with an abrupt reduction at 800 o C, whereas the annealing in argon does not induce significant changes but results in two clear minima at 300 o C and 800 o C. These effects are explained with crystal improvement at low temperature (300 o C) and successive dopant activation at higher temperature (800 o C). Furthermore, an anomalous surface flattening at 800 o C was observed. The obtained results suggest that the annealing procedure does allow to decrease the resistivity and roughness of as-grown ZnO:Ga films, what would be beneficial for the application of PEMOCVD-grown ZnO thin films for the formation of abrupt junctions in p-n device structures.

ZnO materials and surface tailoring for biosensing

“…A smoother ZnO film is obtained, upon initial thermal annealing at 300 °C (Figure 9b). The clearly observed smoothing is suggested to be due to elimination of strain inside the film, and to partial melting and redistribution of the grains, consistent with earlier studies, where 300 °C is reported as the appropriate temperature for decreasing the roughness of the ZnO film surface (94). Further annealing results in an increased grain size and a well developed morphology is obtained at 500°C (Figure 9c).…”

“…The grain size grows as a function of annealing temperature, as expected, due to Oswald ripening. This process has previously been studied in detail, for ZnO films (94). A smoother ZnO film is obtained, upon initial thermal annealing at 300 °C (Figure 9b).…”

Morphology engineering of ZnO nanostructures

“…Finally, at high temperatures, the sheaves of the nanorods are still highly oriented and perfectly located, however their surface is rough. That can be a result of the Zn and O species re-evaporation during the growth, what is expected for ZnO and was earlier observed for growth temperatures over 500 °C [26].…”

Effects of Ar vs. O2 ambient on pulsed-laser-deposited Ga-doped ZnO

“…However, as the oxygen pressure is increased, the film resistivity increases [6,7]. Subsequent anneals in air further increase the resistivity [2,8]. Thermodynamic arguments suggest that the high resistivity obtained in excess oxygen may be a result of more compensating acceptor-like point defects, including the Zn vacancy V Zn , the O interstitial O I , and the O anti-site O Zn , as their formation energies will decrease in oxygen-rich growth environments [9].…”