Fabrication of a low-threading-dislocation-density AlxGa1−xN buffer on SiC using highly Si-doped AlxGa1−xN superlattices

An in situ technique to reduce the threading dislocation density (TDD) of an AlxGa1−xN buffer within submicron-thick growth is demonstrated using metalorganic vapor-phase epitaxy. We achieved a marked reduction in the TDD of the AlGaN buffer on a SiC substrate by inserting superlattices (SLs) consisting of highly Si-doped AlGaN and undoped AlGaN layers. The TDD of AlGaN decreased from 2×1010 to 7×107 cm−2 by inserting SLs with total growth thickness of 0.8 μm. The Si incorporation in the highly Si-doped AlGaN layers of the SLs was estimated to be approximately 1.2×1020 cm−3 (0.24%). This is strictly an in situ technique that does not require complicated fabrication processes, and the surface is kept flat throughout the entire growth. This method is especially useful on SiC wafers to prevent cracks in a thin growth layer.