Elsevier

Applied Surface Science

Volume 258, Issue 6, 1 January 2012, Pages 2177-2181
Applied Surface Science

The electrical, optical and magnetic properties of Si-doped ZnO films

https://doi.org/10.1016/j.apsusc.2011.02.093Get rights and content

Abstract

In this paper, the influences of Si-doping on electrical, optical and magnetic properties of ZnO films have been systematically investigated. It is found that the resistivity of the films decreases from 3.0 × 103 to 6.2 × 10–2 Ωcm with Si-doping due to the increase of carrier concentration. The bandgap of ZnO films increases from 3.28 to 3.52 eV with increasing of Si concentration, which is found to be due to the collective effects of bandgap narrowing and Burstein–Moss effect induced by high carrier concentration. With increase of Si concentration, the near band edge (NBE) emission decreases due to the deterioration of crystal quality, while the yellow emission enhances due to the increase of extrinsic impurity or defects. The additional Si-doping has a profound influence on the enhancement of magnetic property and the maximum magnetic moment of 2.6 μB/Si is obtained. The ferromagnetic ordering is seen to be correlated with carrier concentration and structural defects.

Highlights

► The resistivity of the ZnO films can significantly decrease by Si-doped. ► The bandgap of the film increases to 3.52 eV when Si concentration is of 6%. ► Yellow emission enhances due to the increase of extrinsic impurity or defects. ► The maximum magnetic moment of 2.6 μB/Si is obtained.

Introduction

Znic oxide (ZnO), a well-known wide and direct bandgap semiconductor [1], [2], [3], [4], can be used as diluted magnetic semiconductors (DMSs) and light-emitting diodes due to its room temperature (RT) ferromagnetism (FM) and luminescence property when it is doped with appropriate transition metals (TM) [5], [6], [7]. It has been demonstrated that the ferromagnetic ordering in TM-doped ZnO is correlated with carrier concentration and the structural defects [8], [9], [10]. Recently, RTFM has been observed in carbon-doped ZnO, which indicates that RTFM also exists in non-TM doped ZnO [11], [12], [13]. Silicon, being in the same group with carbon, may also act as an effective dopant to induce the RTFM in ZnO. It has been reported that Si atoms act as effective donors in Si-doped ZnO films prepared by magnetron sputtering depositions [14]. According to Liu et al. [15], donor defects would enhance the FM in TM-doped ZnO films, thus Si may act as an effective dopant to enhance the RTFM in ZnO films.

In addition, silicon is a well known dopant that predominantly occupies cation sites in III–V semiconductors to improve their electrical and optical properties [16]. Similarly, using Si as a dopant material in ZnO might also tune its electrical and optical properties. It has been reported that the intrinsic and extrinsic defects have a profound influence on the luminescence properties of ZnO [17], [18], [19]. Silicon, as a dopant material in ZnO, might also introduce intrinsic and extrinsic defects which affect the luminescence properties of ZnO. So far, some works have been done on the electronic structures and transparent conductive properties in Si-doped ZnO [14], [20], [21], [22]. However, few works on the luminescence and magnetic properties of Si-doped ZnO films has been reported, which might enhance its usefulness in Si-related devices.

In this work, many experiments are used to study the structural, electrical, optical and magnetic properties of Si-doped ZnO films. It is found that a trace amount of additional Si-doping plays an important role in the enhancement of the electrical and ferromagnetic properties, and the Si-doping also influence the luminescence property significantly.

Section snippets

Experimental details

Undoped ZnO, Zn0.99Si0.01O, Zn0.98Si0.02O, Zn0.96Si0.04O and Zn0.94Si0.06O films were prepared on glass, Si (1 0 0) and sapphire substrates at room temperature by direct-current reactive magnetron co-sputtering method, using a zinc target (99.99% purity, 120 mm diameter) attached by several Si chips (99.99% purity). Si chips were distributed uniformly around the sputtering race-track. In order to adjust Si concentration in the deposited films, the sputtering area proportion of Si chips was changed

Results and discussion

Fig. 1 depicts the XRD patterns of Zn1−xSixO (x = 0, 0.01, 0.02, 0.04 and 0.06) films deposited on Si (1 0 0) with the 2θ ranging from 30 to 50°. As can be seen from the figure, both undoped and Si-doped ZnO films have only one peak at ∼34° which is from the diffraction of ZnO (0 0 2) plane. No other peaks can be found in the patterns, indicating that the films have preferred orientation with c-axis normal to the substrate, and Si-doping does not change the wurtzite structure of ZnO films. With

Conclusions

In conclusion, highly transparent and RT ferromagnetic Si-doped ZnO films were prepared by direct-current reactive magnetron co-sputtering method. The experimental results indicate that Si acts as an effective donor in ZnO and donate electrons. The ferromagnetic ordering is seen to be correlated with carrier concentration and structural defects. Because of the collective effects of BM effect and the bandgap narrowing, the bandgap of Si-doped ZnO films increases with increase of Si concentration.

Acknowledgements

The authors are grateful for financial supports from the National Hi-tech (R&D) project of China (Grant Nos. 2007AA03Z426 and 2009AA034001), National Natural Science Foundation of China (Grant Nos. 50871060 and 50772055) and National Basic Research Program of China under Grant No. 2010CB832905.

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