Influences of defects evolvement on the properties of sputtering deposited ZnO:Al films upon hydrogen annealing

Abstract

Understanding how the defects interact with each other and affect the properties of ZnO:Al films is very important for improving their performance as a transparent conductive oxide (TCO). In the present work, we studied the effects of hydrogen annealing on the structural, optical and electrical properties of ZnO:Al films prepared by magnetron sputtering. High resolution transmission electron microscopy observations reveal that annealing at ∼300 oC induces the formation of partial dislocations (PD) and stacking faults (SF), which disrupt the lattice periodicity leading to decreased grain size. Annealing at temperatures above ∼500 oC can remove the PD and SF, but large number of zinc vacancies will be generated. Our results show that when films are annealed at ∼500 oC, the oxygen-related defects (interstitials Oi, etc.) in the as-grown films can be remarkably removed or converted, which lead to increments in the carrier concentration, mobility, and the transmittance in the visible range. At annealing temperatures above 550 oC, the hydrogen etching effect becomes predominant, and Al donors are deactivated by zinc vacancies. We also find an abnormal endothermic process by thermal analysis and an abnormal increase in the resistivity during heating the sample under hydrogen atmosphere, based on which the interaction of Oi with the defects (mainly Al donors and PD) is discussed. It is also demonstrated that by annealing the as-grown AZO films at ∼500 oC under hydrogen atmosphere, high performance TCO films with a low resistivity of 4.48 × 10−4 Ωcm and high transmittance of above 90% in the visible light are obtained.

Room Temperature Strong Emission and Excitonic Enhancement in Multiple‐Stacked Nano‐Porous ZnO Thin Film

“…Here, we can see that the film surface consists of nano‐pores with the different depth indicating the formation of multiple‐stacked porous structure. This feature also might be originated from the etching process by the hydrogen atom . Furthermore, Figure f shows the XRD patterns of as‐prepared and annealed ZnO films.…”

Electrochemical modification of properties of ZnO films

“…It is known that the sheet resistance of ZnO films is decreased by annealing in H 2 . [24][25][26] After the H 2 annealing, the sheet resistances of the AZO-3 wt % and LAZO films were about 10 2 Ω=sq and there were no differences between the two films. Figure 4 shows the sheet resistance of the H 2 -annealed ZnO films during the repetitive electrochemical treatment.…”

Decay mechanisms in CdS‐buffered Cu(In,Ga)Se2 thin‐film solar cells after exposure to thermal stress: Understanding the role of Na

“…One approach to achieve this could be to decrease the absorption losses in the transparent conductive oxide (TCO) used as front contact material by increasing its transparency. For this, it would be of great advantage to be able to work at elevated deposition temperatures and/or to apply a post‐deposition annealing 3–5 . Another possibility to increase device efficiencies even past the single junction Shockley–Queisser limit is to fabricate multi‐junction solar cells by utilizing different wavelength ranges of the incident light spectrum in a stack of two or more solar cells with different bandgap energies.…”