Observation of nitrogen species at Al2O3/NO2/H-diamond interfaces by synchrotron radiation x-ray photoemission spectroscopy

Two nitrogen-related peaks were successfully detected by synchrotron radiation x-ray photoemission spectroscopy (XPS) at the interface of the Al2O3/NO2/H-diamond structure, which is used for metal–oxide–semiconductor field-effect transistors. The 399-eV peak was attributed to the C‒NH2 or C‒N bond, which was formed by electron transfer from the NO2 molecule to the H-diamond surface and subsequent decomposition of NO2 molecules at the H-diamond surface. The 407-eV peak was attributed to NO 3 − bond, which was formed by the decomposition of N2O4 molecules. We confirmed that N species are localized at the interface by changing the photoemission angle in XPS. The N interface density at the (111) interface was about twice that at the (001) interface. This difference is caused by C‒H bond density on different surface orientations. The band alignments were determined to be type II (staggered type), and the valence band offset (ΔEV) was determined to be 3.9 ± 0.1 eV for (001) and 4.3 ± 0.1 eV for (111) surface orientations. These results agree well with the higher hole sheet concentration on the (111) interface than on the (001) interface.