Abstract

The wurtzite GaN and related nitride films are typically grown on sapphire or SiC substrates. However, large lattice-mismatches between GaN and sapphire or SiC can lead to degradation of quality of grown GaN by 16 and 4%, respectively. ZrB2 is a semi-metal compound and has a hexagonal crystal structure. The a-axis lattice constant of ZrB2 is 3.168 Å, which is almost lattice-matched to GaN. The thickness of ZrB2 film is 228 nm which was prepared on a Si(111) substrate by pulsed DC magnetron sputtering deposition. The effects of substrate temperatures ranging from 400 to 550 °C on the microstructure, resistivity and surface roughness of the deposited ZrB2 films were investigated by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), the four-point probe technique and atomic force microscopy (AFM). XRD analysis revealed that the ZrB2 film had a polycrystalline structure and the preferred orientation was along (001) when the substrate temperature was above 450 °C. The relationship between the average grain size of the ZrB2 film and substrate temperatures ranging from 450 to 550 °C forms a downward parabolic function. The minimum average grain size of the ZrB2 film was 10.6 nm when the substrate temperature was 500 °C. The minimum resistivity of the ZrB2 film was 229 µΩ cm when the substrate temperature was 550 °C. The AFM measurements showed the ZrB2 films to have a uniform morphology with a very low surface roughness value of 0.2 nm. In this work, it was found that a uniform surface morphology and preferred orientation along (001) of the ZrB2 film on Si(111) could be obtained through pulsed DC magnetron sputtering when the substrate temperature was above 450 °C. This mirror-polished ZrB2 buffer layer is a good candidate for GaN film growth on Si(111) wafers.

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