Abstract
We demonstrate growing nitrogen-polar (N-polar) GaN epilayer on c-plane sapphire using a thin AlN buffer layer by metalorganic chemical vapor deposition. We have studied the influence of the AlN buffer layer on the polarity, crystalline quality, and surface morphology of the GaN epilayer and found that the growth temperature of the AlN buffer layer played a critical role in the growth of the GaN epilayer. The low growth temperature of the AlN buffer results in gallium-polar GaN. Even a nitridation process has been conducted. High growth temperature for an AlN buffer layer is required to achieve pure N-polarity, high crystalline quality, and smooth surface morphology for a GaN epilayer.
Highlights
Nitrogen-polar (0001) (N-polar) GaN is attractive in III-nitride research because of its opposite spontaneous polarization field direction compared to gallium-polar (Ga-polar) structures
We report on the growth of an N-polar GaN epilayer on c-plane sapphire using a thin AlN buffer layer by metalorganic chemical vapor deposition (MOCVD)
We studied the influence of the AlN buffer layer on the polarity, crystalline quality, and surface morphology of the GaN epilayer and found that the growth temperature of the AlN buffer layer played an important role in achieving purely N-polar GaN with high crystalline quality and a smooth surface
Summary
Nitrogen-polar (0001) (N-polar) GaN is attractive in III-nitride research because of its opposite spontaneous polarization field direction compared to gallium-polar (Ga-polar) structures. The use of low-temperature GaN as a nucleation layer substrate has been well developed and understood to achieve N-polar GaN on sapphire [11,12,13,14]. The growth mechanism of using an AlN nucleation layer to obtain N-polarity of a GaN epilayer is unclear. We report on the growth of an N-polar GaN epilayer on c-plane sapphire using a thin AlN buffer layer by metalorganic chemical vapor deposition (MOCVD). A high growth temperature above 850 ◦ C for the AlN buffer layer is required to achieve pure N-polarity, high crystalline quality, and smooth surface morphology in a GaN epilayer
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