The impact of negative oxygen ion bombardment on electronic and structural properties of magnetron sputtered ZnO:Al films

Bikowski, André; Welzel, Thomas; Ellmer, K.

doi:10.1063/1.4811647

Cited by 66 publications

(53 citation statements)

References 21 publications

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“…On the other hand, the intensity of the broad orange emissions centered at 650 and 750 nm, which are mainly related to deep-level emissions through oxygen interstitial, [44][45][46][47] decreases at a large x. This is because the flux of energetic negative oxygen ions, which cause the formation of oxygen interstitial in ZnO, 24 decreases with increasing x.…”

Section: With Buffer Layersmentioning

confidence: 93%

“…In magnetron sputtering, there are many high-energy particles, such as negative oxygen ions and recoil Ar, which cause defect formation in ZnO films. 24,25 Since both particles are accelerated in the cathode sheath, 26,27 the flux of the energetic particles can be reduced by taking the off-axis configuration where the substrate is positioned out of the highenergy particles originating from the targets. Here, aiming at realizing high-quality ZnO films with a low defect density, the effects of off-axis configuration together with NMC buffer layers are investigated through the analysis of the properties of ZnO films fabricated at various substrate/target configurations.…”

Section: Introductionmentioning

confidence: 99%

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Off-axis sputter deposition of ZnO films on c-sapphire substrates by utilizing nitrogen-mediated crystallization method

et al. 2014

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Abstract. High-quality epitaxial ZnO films on c-plane sapphire substrates have been obtained by utilizing an offaxis sputtering configuration together with buffer layers prepared via nitrogen-mediated crystallization (NMC). The role of NMC buffer layers is to provide high density of nucleation site and, thus, to reduce the strain energy caused by the large lattice mismatch (18%) between ZnO and sapphire. The NMC buffer layers allow two-dimensional growth of subsequently grown ZnO films, being particularly enhanced by employing an off-axis sputtering configuration in which the substrate is positioned out of the high-energy particles, such as negative oxygen ions originating from the targets. As a result, ZnO films with smooth surfaces (root-mean-square roughness: 0.76 nm) and a high electron mobility of 88 cm 2 ∕V · s are fabricated. Photoluminescence spectra of the ZnO films show strong near-band-edge emission, and the intensity of the orange-red defect emission significantly decreases with increasing horizontal distance between the target and the substrate. From these results, we conclude that off-axis sputtering together with NMC buffer layers is a promising method for obtaining high-quality epitaxial ZnO films. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

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Section: With Buffer Layersmentioning

confidence: 93%

Section: Introductionmentioning

confidence: 99%

Off-axis sputter deposition of ZnO films on c-sapphire substrates by utilizing nitrogen-mediated crystallization method

et al. 2014

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“…Tominaga et al [132] confirmed this effect for AZO films prepared by RF magnetron sputtering and related it to the bombardment of the film with negative oxygen ions coming from the target. This negative oxygen ion bombardment can introduce acceptor defects, such as oxygen interstitials into the growing film, and therefore decrease the charge carrier concentration as reported by Bikowski et al [9]. They observed a minimum in the resistivity for a certain substrate temperature that depends on the sputter method.…”

Section: Sputter Deposition Of Azo Thin Filmsmentioning

confidence: 76%

“…The bombardment of the growing film with negative oxygen ions is believed to cause the deactivation of charge carriers due to the formation of insulating secondary phases [8,9,63]. The formation of secondary phases has been reported to increase at high substrate temperatures due to the preferential desorption of Zn [63].…”

Section: Paper 2: Restoring the Properties Of Transparent Al-doped Znmentioning

confidence: 99%

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Deposition of Al-doped ZnO films by high power impulse magnetron sputtering

Mickan¹

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Transparent conducting oxides (TCOs) are an important class of materials with many applications such as low emissivity coatings, or transparent electrodes for photovoltaics and flat panel displays. Among the possible TCO materials, Al-doped ZnO (AZO) is studied due to its relatively low cost and abundance of the raw materials. Thin films of AZO are commonly produced using physical vapour deposition techniques such as magnetron sputtering. However, there is a problem with the homogeneity of the films using reactive direct current magnetron sputtering (DCMS). This homogeneity problem can be related to the bombardment of the growing film with negative oxygen ions, that can cause additional acceptor defects and the formation of insulating secondary phases. In this work AZO films are deposited by high power impulse magnetron sputtering (HiPIMS), a technique in which high instantaneous current densities are achieved by short pulses of low duty cycle.In the first part of this thesis, the possibility to improve the homogeneity of the deposited AZO films by using HiPIMS is demonstrated. This improvement can be related to the high instantaneous sputtering rate during the HiPIMS pulses, so the process can take place in the metal mode. This allows for a lower oxygen ion bombardment of the growing film, which can help to avoid the formation of secondary phases. Another problem of AZO is the stability of the properties in humid environments. To assess this problem, the degradation of the electrical properties after an aging procedure was investigated for films deposited by both DCMS and by HiPIMS. A method was proposed, to restore the properties of the films, using a low temperature annealing under N 2 atmosphere. The improvement of the electrical properties of the films could be related to a diffusion process, where water is diffusing out of the films. Then, the influence of the substrate temperature on the properties of AZO films deposited by HiPIMS was studied. The electrical, optical and structural properties were found to improve with increasing substrate temperature up to 600• C. This improvement can be mostly explained by the increase I in crystalline quality and the annealing of defects. Finally, the deposition of AZO films on flexible PET substrates was investigated. The films are growing as a thick porous layer of preferentially c-axis oriented columns on top of a thin dense seed layer. The evolution of the sheet resistance of the films after bending the films with different radii was studied. There is an increase in the sheet resistance of the films with decreasing bending radius, that is less pronounced for thicker films. II Populärvetenskaplig sammanfattningFör många viktiga tillämpningar i vårt moderna liv, såsom skärmar till mobiltelefoner eller solceller, är det nödvändigt att ha ett transparent material som har en elektrisk ledningsförmåga. Att både vara transparent och vara elektriskt ledande är en ovanlig materialegenskap. Material som är elektriskt ledande, såsom metaller, är vanligtvis inte transp...

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Possibilities of Increasing the Usability of Sputtered AZO Films as a Transparent Electrode

Novák

2019

Physica Status Solidi (a)

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Aluminum-doped zinc oxide (AZO) is a suitable material for use as transparent electrode. Due to its lower price it is applied in the production of silicon solar cells. However, it is difficult to obtain suitable electrical properties at low deposition temperatures. Moreover, the AZO films with low thickness exhibit significantly higher average resistivity, which limits their usability, especially if they are prepared on flexible substrates. A lot of effort is invested to replace indium tin oxide (ITO) to a much greater extent now, since Indium is rare and its price is rising, thus the preparation of lowthickness AZO films at low temperature is also subject of intense research. The presented paper summarizes the reported results, discusses the causes of the differences between ITO and AZO films, and suggests the direction of research and the potential solution that should lead to increased usability of AZO films and also possible replacement of ITO films.

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The impact of negative oxygen ion bombardment on electronic and structural properties of magnetron sputtered ZnO:Al films

Cited by 66 publications

References 21 publications

Off-axis sputter deposition of ZnO films on c-sapphire substrates by utilizing nitrogen-mediated crystallization method

Off-axis sputter deposition of ZnO films on c-sapphire substrates by utilizing nitrogen-mediated crystallization method

Deposition of Al-doped ZnO films by high power impulse magnetron sputtering

Possibilities of Increasing the Usability of Sputtered AZO Films as a Transparent Electrode

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