Growth of Al–N codoped p-type ZnMgO thin films on different substrates

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Abstract

Al–N codoped p-type ZnMgO thin films were prepared on three different substrates, namely glass, quartz, and silicon. Significant differences in the crystallinity, surface morphology, and electrical properties on these substrates were investigated by means of x-ray diffraction, field-emission scanning electron microscopy, and Hall-effect measurements. It is demonstrated that the Al donor enhances the incorporation of the N acceptor, resulting in better p-type conductivity. The incorporation of the N acceptor, as well as the Al and Mg, was confirmed x-ray photoelectron spectroscopy. Transmittance and photoluminescence spectra suggested a wider bandgap for the ZnMgO thin films in comparison with ZnO, which is believed to be the result of the incorporation of Mg.

Introduction

Due to a direct bandgap of 3.37 eV and large exciton binding energy of 60 meV at room temperature, ZnO is considered as a promising material for use in short wavelength light-emitting diodes, laser diodes, and detectors [1]. However, several issues remain to be resolved before further development of high efficiency ZnO-based devices can proceed, such as the lack of reliable p-type materials and high quality ternary compounds (ZnMgO and ZnCdO) [2]. Recently, considerable worldwide efforts have been devoted to the growth of stable p-type ZnO [3], [4], [5], [6], [7], [8], [9], [10]. The investigation on p-type ZnMgO, however, is relatively limited [11], [12], [13]. On the other hand, there are few systematic studies on p-type materials grown on different substrates. It is expected that the properties of ZnO as well as ZnMgO films may differ on the different substrates. Also, different substrates are required for diverse applications, e.g. glass and quartz substrates are suitable for growth of low cost transparent conducting films; silicon wafers are suitable for optoelectronics applications and high power devices. In these regards, systematic investigations on p-type ZnMgO on different substrates are strongly demanded. In the previous studies, it has been theoretically and experimentally demonstrated that codoping of donor Al will promote the incorporation of N acceptors, leading to better p-type conductivity in ZnO [14], [15], [16]. In this work, by adopting the Al–N codoping method, p-type ZnMgO thin films were grown on different substrates, in an attempt to better understand the p-type behavior.

Section snippets

Experiments

Al–N codoped ZnMgO thin films were grown on three different substrates, namely glass, quartz and n-type silicon wafers with the resistivity of 10 Ω cm, by a dc reactive magnetron sputtering method. A ternary Zn0.94Mg0.05Al0.01 alloy, with a purity of 99.99%, was used as the sputtering target. The vacuum chamber was evacuated to a base pressure of 10−3 Pa. Then Ar (99.99%), O2 (99.99%), and N2O (99.99%) were introduced into the chamber with a mole ratio of 1:1:1 and the sputtering pressure was

Results and discussion

The XRD patterns of ZnMgO thin films grown on different substrates are illustrated in Fig. 1. All the patterns show one dominant peak corresponding to the ZnO (002) plane, suggesting a c-axis preferential orientation. However, the glass sample also shows another peak corresponding to the ZnO (100) plane, which indicates a decreasing crystallinity. The (002) peak is much stronger on the silicon than that on the glass and quartz substrates. Also, the value of the full width at half-maximum (FWHM)

Conclusion

In summary, we have demonstrated reproducible growth of Al–N codoped p-type ZnMgO thin films on three different substrates, namely glass, quartz, and n-type silicon. The effects of the substrate type on the crystallinity, surface morphology, and electrical properties were discussed. A wider bandgap for the ZnMgO due to the incorporation of Mg was confirmed by transmission and PL spectra. The realization of p-type ZnMgO thin films will further advance the development of ZnO-based light-emitting

Acknowledgements

This work was supported by National Basic Research Program of China under Grant No. 2006CB604906 and National Natural Science Foundation of China under Contract Nos. 50532060 and 90601003.

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