ROLE OF INTERFACIAL-CHARGE IN THE GROWTH OF GAN ON ALPHA-SIC

The growth of GaN and AlN films on (0001) substrates of 6H-SiC has pro duced high-quality opto-electronic films. The SiC surface at the inter face with GaN or AlN is either Si-terminated or C-terminated, and the Si-terminated interface is known to be the better substrate, producing higher-quality films. The polarity of the interface is important, as recognized by Sasaki and Matsuoka. We propose that the main relevant p arameter for characterizing the interface and its potential for produc ing high-quality opto-electronic GaN or AIN films is the interfacial c harge, which leads to the best films when the charge is positive and r elatively large. The positive charge reduces the size of the N ions at the interface and hence improves the Local lattice match. (The charge s are approximately -0.45 \e\ and +0.55 \e\ on the interfacial N and S i atoms, respectively.) Therefore, while the polarity of the interface is important, the polarity's effect on the local lattice mismatch is what leads to a high-quality interface. These ideas are consistent wit h XPS data and are supported by electronegativity arguments, by calcul ations for ordinary mono-bonded GaN/SiC superlattices (with id-Si and Ga-C interfaces) and by computations for superlattices with tri-bonded interfaces. We predict that the tri-bonded N-Si interface of GaN/SiC should produce excellent GaN and AlN films.