Effect of oxygen pressure and post-annealing on the properties of reactively sputtered zinc oxide thin films Fatima Moutai a,b , Mesbah Elyaagoubi a , Ahmad Afkir a , Rajaa Rochdi c , Abdelaziz El Boujlaidi a , Nabil Rochdi a,⇑ a Cadi Ayyad University, Faculty of Sciences Semlalia, Department of Physics, Prince Moulay Abdellah Avenue, PO Box 2390, 40000 Marrakesh, Morocco b Cadi Ayyad University, Faculty of Sciences and Techniques, Department of Applied Physics, Prince Abdelkarim Elkhattabi Avenue, PO Box 549, 40000 Marrakesh, Morocco c Mohammed V University, Faculty of Sciences of Rabat, Department of Chemistry, Ibn Batouta Avenue, PO Box 1014, 10106 Rabat, Morocco article info Article history: Received 30 May 2020 Received in revised form 22 July 2020 Accepted 26 July 2020 Available online xxxx Keywords: Zinc oxide thin films Reactive radio-frequency sputtering X-ray diffraction Optical transmission Scanning electron microscopy Energy dispersive X-ray spectroscopy abstract Using radio-frequency sputtering in the reactive regime at a fixed radio-frequency power of 200 W, we deposited zinc oxide thin films at room temperature on glass substrates in argon-oxygen sputtering atmospheres with different sputtering durations, and various oxygen contents from 20% to 70%. X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and transmittance spec- trophotometry were used to probe structural, morphological, chemical and optical properties of as-grown and post-annealed thin films in air at medium temperatures (up to 500 °C). The as-grown samples were found to present a hexagonal crystalline structure with a major (0 0 2) orientation and direct bandgap energies ranging from 3.27 to 3.3 eV. The post-annealing results in the improvement of crystallinity of ZnO thin films deposited at low oxygen contents and in the deterioration then the recrystallization of films deposited in oxygen-rich plasma. The optimal properties and thermal stability were obtained for 30% of oxygen in the sputtering environment, with an annealing-induced shrinkage of the bandgap smal- ler than 100 meV. Ó 2020 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 5thEuro-Mediterranean Conference on Materials and Renewable Energies. 1. Introduction Since the emergence of the semiconductor industry in the mid- dle of last century, numerous research works have been devoted to the development of downscaled, cost-competitive, and more per- formant devices exhibiting new properties and functionalities. Therefore, the processing and the characterization of thin films have naturally gained a growing interest, boosted by the maturity of elaboration technology and the variety of prospective applica- tions [1–7]. In this respect, the films homogeneity, defects and strain related mechanisms, electronic properties, and surface/in- terfaces reactivity have been among the main aspects to address [8–16]. The zinc oxide (ZnO) is one of the materials that have attracted a great interest over the last past decades mainly due to its low- cost, its non-toxicity, and its remarkable properties and advantages over other transparent conductive oxides and transition metal oxi- des. This II-VI semiconductor possesses a large direct bandgap and a high binding energy of free excitons of about 60 meV at room temperature, making it a promising material for optoelectronics and photovoltaics. In this respect, a wide variety of ZnO-based optodevices (such as light emitting diodes and photodetectors) operating at ambient were successfully achieved [17–19]. In addi- tion, ZnO presents outstanding electrical and optical properties (such as a high electrical conductivity, and an important optical transparency in the visible region), enhanced chemical stability and radiation hardness, and important catalytic properties. Thus, ZnO is regarded as an interesting material in the fields of electron- ics, piezoelectric devices, and diluted magnetic semiconductors for instance [20–24]. As a consequence, numerous fabrication tech- niques were investigated to elaborate ZnO materials such as chem- ical vapor deposition, pulsed laser deposition, electrodeposition, and sol–gel [25–28]. In this work, we used reactive radio-frequency (RF) sputtering technique [29,30] to deposit ZnO thin films at room temperature (RT) on glass substrates in oxygen-argon plasmas. The elaborated https://doi.org/10.1016/j.matpr.2020.07.607 2214-7853/Ó 2020 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 5thEuro-Mediterranean Conference on Materials and Renewable Energies. ⇑ Corresponding author. E-mail address: nabil.rochdi@uca.ma (N. Rochdi). Materials Today: Proceedings xxx (xxxx) xxx Contents lists available at ScienceDirect Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr Please cite this article as: F. Moutai, M. Elyaagoubi, A. Afkir et al., Effect of oxygen pressure and post-annealing on the properties of reactively sputtered zinc oxide thin films, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.07.607