Observation of a negative electron affinity for heteroepitaxial AlN on α(6H)-SiC(0001)

This study demonstrates the presence of a negative electron affinity (NEA) surface on AlN was grown on α(6H)-SiC. Heteroepitaxial AlN was grown on α(6H)-SiC(0001) substrates by molecular beam epitaxy techniques. The surface electronic states were characterized by ultraviolet photoemission obtained at surface normal. The observation of a sharp spectral feature at the lowest energy of the emitted electrons is an indication of a surface with a negative electron affinity. In addition, the trend of the NEA feature was examined as a function of annealing. 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 presented.