HRTEM investigation of the interface between AIN and SiC

Epitaxial thin films of the group III nitrides play an increasingly important role in the fabrication of high-efficiency light emitting diodes in the range between yellow and blue. Growth of such films on sapphire requires the use of low temperature buffer layers of AIN or GaN. Silicon carbide has a much closer lattice parameter match than sapphire to AIN, and promises to produce better AIN layers. Since the atomic arrangement at the interface between AIN and SiC determines the degree of perfection of the epitaxial layer, we have attempted to determine the structure of this interface by hign-resolution transmission electron microscopy. Devices were grown by MOCVD; AIN was deposited on the Si-face of α-6H SiC, followed by GaN. The specimen was cut for HRTEM observation in the SiC projection, mechanically thinned to 20μm and ion-milled to electron transparency. Observations were made using the NCEM JEOL ARM-1000 operated at 800keV. Images were obtained at a specimen thickness of 85A (determined by extrapolation to the first extinction distance of the wedge). The most-useful defocus was −1050Å at which the important spacings from both SiC and AIN are passed with the same phase (fig.1).