Characterization of electron emitting surfaces of diamond and III-V nitrides

Wide band gap semiconductors such as diamond and the diamond-related materi als of GaN and AlN, exhibit small or even negative electron affinities. Rec ent results have shown that surface treatments will modify the electron aff inity of diamond, causing it to have a negative electron affinity (NEA). Fo r the III-V nitrides of GaN and AIN, results indicate a NEA for some surfac es of AIN and an electron affinity of 3.3 eV for GaN. Alloys of AlGaN exhib it a composition-dependent electron affinity that tends to a value of zero at similar to 70% AlN. In this study we describe approaches for the charact erization of these surfaces using UV photoemission spectroscopy (UPS), posi tion-dependent field emission and photo-electron emission microscopy (PEEM) . Measurements are presented of field emission from single crystal p-type ( boron doped) diamond with various surface processes. The field emission res ults are correlated with the surface processes used to establish a NEA surf ace. The field emission threshold of nitrogen-doped samples is significantl y higher than that of p-type diamond; in fact, most surfaces are severely d amaged during the emission measurement. The PEEM technique, which combines aspects of UPS and field emission, images the emitted electrons allowing us to establish a true relationship between the emission and the surface morp hology. PEEM results for both diamond and nitride surfaces are presented.