A study of 2DEG properties in AlGaN/GaN heterostructure using GaN/AlN superlattice as barrier layers grown by MOCVD

GaN/AlN superlattice (SL) structures working as quasi-AlGaN barrier layers for GaN-based high electron mobility transistor have been grown by metal-organic chemical vapor deposition. The influences of the SL period thickness on the electrical properties of two-dimensional electron gas (2DEG) have been investigated. It is found that the sheet carrier concentration increases as the increase in period thickness at a certain equivalent Al composition, and the electron mobility is strongly dependent on the AlN thickness in a period. We consider that AlN transits from two-dimensional growth to three-dimensional (3D) growth when AlN thickness exceeds its critical thickness. The 3D growth mode results in rough interface and surface morphology, which rapidly decreases the electron mobility due to the increase in interface roughness scattering and dislocation scattering to 2DEG.