Interfacial engineering for semi-insulating GaN/sapphire template with low dislocation density

• Interfacial engineering for semi-insulating and low-TDD GaN epilayer on sapphire. • Ultrathin sputtered AlN interfacial layer is nano-pixelated into discrete islands. • Adequate 3D growth of GaN on AlN buffer results in a low TDD of 2.7 × 10 8 cm −2 . • EELS mapping reveals O concentration plummets at GaN/AlN interface. • GaN epilayer grown on the ultrathin AlN buffer has a high R s of 2.43 × 10 11 Ω/sq. Achieving semi-insulating (SI) GaN epilayers with low threading dislocation density (TDD) on sapphire substrates is critically important but challenging for electronic and optoelectronic devices. To obtain low-TDD SI GaN within a thin layer, herein, we performed interfacial engineering for early regulating dislocation and impurity behaviors. It is found that introducing an ultrathin (10 nm) sputtered AlN interfacial buffer layer can effectively suppress dislocations and oxygen (O) impurities. Compared with GaN and thick AlN buffer layers, the ultrathin AlN buffer layer can be nano-pixelated into discrete islands with higher density, ensuring an adequate three-dimensional growth with locally quick coalescence. Hence, the TDD value of the GaN epilayer was rapidly decreased to a low level at the earlier stage of growth. In addition, benefiting from the high diffusion barrier of O in AlN, AlN buffers demonstrate a superior blocking effect of O impurities over GaN buffer, even if the thickness is only 10 nm. Finally, GaN epilayer with a TDD value of 2.7 × 10 8 cm −2 and a sheet resistance of 2.43 × 10 11 Ω/sq can be achieved at the same time. The interfacial buffer engineering provides a simple and effective strategy to obtain high-crystalline-quality SI materials, without additional negative effects introduced.