Growth of N-Face Polarity III-Nitride Heterostructures on C-Face 4H-SiC by Plasma-Assisted MBE

In this work, we present the growth and characterization of N-face polarity GaN layers and AlxGa1-xN/GaN heterostructures by plasma-assisted MBE on NOVASIC-polished C-face 4H-SiC. III-nitrides grown on this substrate exhibits N-face polarity, independent of the buffer layer, either AlN or GaN, and of the III/V ratio. This polarity remains unchanged during the growth of AlxGa1-xN/GaN heterostructures. To prevent the accumulation of Ga droplets on the surface, growth was performed with less than 1 monolayer (ML) of Ga on the surface. Cross-section TEM images of N-face polarity AlN/GaN heterostructures reveal an interface thickness of 2-3 ML, in contrast to similar Ga-face polarity structures where the interface thickness was measured to be < 1 ML. Photoluminescence emission of N-face polarity structures is about ten times more intense than that of their best Ga-face counterparts, indicating a reduction of non-radiative recombination centers. Stimulated emission has been achieved in AlGaN/GaN double heterostructures with a threshold similar to that of Ga-face polarity heterostructures and lower optical losses in the waveguide.