Abstract
In this study, we developed a novel growth method named “Flux-Film-Coated (FFC) sputtering.” In this method, nitrogen radicals were supplied to the Al–Sn flux at around 600 °C followed by the deposition of an Al–Sn metal film on a sapphire substrate as flux, which resulted in the growth of high-quality AlN films. The nitrogen radical, which is the source of nitrogen for the growth of AlN, was generated by the radio frequency plasma in a nitrogen atmosphere. Using a zirconia target in the plasma generation process, nitrogen radicals were easily generated because the zirconia was not etched in a pure nitrogen atmosphere, which enabled us to fabricate the AlN film using the flux method in the sputtering chamber in a single step. The crystallinity of the synthesized AlN determined using the FFC-sputtering method was remarkably improved when compared with that of the AlN film deposited using the reactive sputtering method.
Highlights
AlN has outstanding physical properties such as wide bandgap, similar lattice constant with AlGaN, and high thermal conductivity, which are the reasons for the demand of high-quality AlN substrates
We attempted to grow AlN films by supplying nitrogen radicals generated using a zirconia target in a nitrogen atmosphere into a molten Al–Sn film deposited on sapphire substrates
The perfect c-axis AlN film was successfully grown on a sapphire (0002) substrate by the FFC-sputtering method
Summary
AlN has outstanding physical properties such as wide bandgap, similar lattice constant with AlGaN, and high thermal conductivity, which are the reasons for the demand of high-quality AlN substrates. Some growth methods for AlN substrates have been studied, such as the sublimation method, high-pressure growth, hydride vapor-phase epitaxy, and solution growth.. Miyake et al reported the growth of highquality AlN films with a narrow full width half maximum (FWHM) during the rocking curve measurement. They found a way to grow high-quality metal–organic vapor-phase epitaxy (MOVPE)AlN films by combining AlN buffer layers and annealing them with N2–CO.. We developed a novel technique for growing AlN films on sapphire by combining flux growth with an Al–Sn melt and the sputtering method. Nitrogen plasma was used as the nitrogen source because the solubility of nitrogen radicals in the molten metal is significantly higher than that of nitrogen molecules. Based on this phenomenon, Dyck et al successfully grew GaN [000l] films on sapphire with nitrogen plasma, and they obtained GaN film with 50 μm thickness. We attempted to grow AlN films by supplying nitrogen radicals generated using a zirconia target in a nitrogen atmosphere into a molten Al–Sn film deposited on sapphire substrates
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