Growth of Al_xGa_1-xN/In_yGa_1-yN hetero structure on AlN/sapphire templates exhibiting Shubnikov-de Haas oscillation

We fabricated successfully heterostructures of AlGaN/GaN and AlGaN/InGaN/GaN on AlN template/c-sapphire exhibiting the Shubnikov-de Haas (SdH) oscillation in the magnetic field at lower temperatures. In Al_xGa_1-xN/GaN system, the carrier density of two-dimensional electron gas (2DEG) was controlled from 4.0 × 10¹² to 9.0 × 10¹² cm⁻², which was consistent with the theoretical simulation, with increase of Al composition in AlGaN barrier layer. In AlGaN/InGaN/GaN system, the surface morphology and alloy disorder on the InGaN were properly defined. The effective mass of 2DEG at the Al_0.22Ga_0.78N/In_0.04Ga_0.96N interface was estimated to be 0.24 m₀ from the temperature dependence of SdH oscillation amplitude. Although the effective mass was comparable to that of AlGaN/GaN heterostructure, the mobility of 2DEG at the InGaN was drastically degraded in spite of the slight amount of indium incorporation. This reduction was attributed to larger scattering probably due to the interface roughness of InGaN layer caused by the step meandering and/or the potential fluctuation caused by random incorporation of indium atoms.