Plasma-assisted molecular beam epitaxy of ZnO on in-situ grown GaN/4H-SiC buffer layers

Abstract

Plasma-assisted molecular beam epitaxy (MBE) was used to grow ZnO(0001) layers on GaN(0001)/4H-SiC buffer layers deposited in the same growth chamber equipped with both N- and O-plasma sources. The GaN buffer layers were grown immediately before initiating the growth of ZnO. Using a substrate temperature of 440°C–445°C and an O₂ flow rate of 2.0–2.5 sccm, we obtained ZnO layers with smooth surfaces having a root-mean-square roughness of 0.3 nm and a peak-to-valley distance of 3 nm shown by AFM. The FWHM for X-ray rocking curves recorded across the ZnO(0002) and ZnO($\mathbf{10}\overline{\mathbf{1}}\mathbf{5}$) reflections were 200 and 950 arcsec, respectively. These values showed that the mosaicity (tilt and twist) of the ZnO film was comparable to corresponding values of the underlying GaN buffer. It was found that a substrate temperature >450°C and a high Zn-flux always resulted in a rough ZnO surface morphology. Reciprocal space maps showed that the in-plane relaxation of the GaN and ZnO layers was 82.3% and 73.0%, respectively and the relaxation occurred abruptly during the growth. Room-temperature Hall-effect measurements showed that the layers were intrinsically n-type with an electron concentration of 10¹⁹ cm^–3 and a Hall mobility of 50 cm²·V^–1·s^–1.

Keywords

ZnO / molecular beam epitaxy (MBE) / epitaxy

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Acknowledgements

This work was supported by the Swedish Research Council (Grant DNR 2009-4903). It was also partly supported by a grant from the Department of Microtechnology and Nanoscience (MC2) at Chalmers University of Technology.

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2014 Higher Education Press and Springer-Verlag Berlin Heidelberg