OBSERVATION OF A NEGATIVE ELECTRON-AFFINITY FOR HETEROEPITAXIAL ALN ON ALPHA(6H)-SIC(0001)

This study demonstrates the presence of a negative electron affinity ( NEA) surface on AlN was grown on alpha(6H)-SiC. Heteroepitaxial AlN wa s grown on alpha(6H)-SiC(0001) substrates by molecular beam epitaxy te chniques. The surface electronic states were characterized by ultravio let photoemission obtained at surface normal. The observation of a sha rp spectral feature at the lowest energy of the emitted electrons is a n indication of a surface with a negative electron affinity. In additi on, the trend of the NEA feature was examined as a function of anneali ng. The surface Fermi level is found to be near the middle of the AlN gap, and a possible band alignment between the AlN and SiC is presente d.