AVS 46th International Symposium
    Electronic Materials and Processing Division Monday Sessions
       Session EM-MoA

Paper EM-MoA3
Negative Electron Affinity and Electron Emission at Cesiated GaN and AlN Surfaces

Monday, October 25, 1999, 2:40 pm, Room 608

Session: Nitride Processing and Characterization
Presenter: C.I. Wu, Princeton University
Authors: C.I. Wu, Princeton University
A. Kahn, Princeton University
Correspondent: Click to Email
We present a systematic study of electron affinity and secondary electron emission at clean and cesiated surfaces of p-type GaN and (nominally n-type) AlN using ultraviolet and x-ray photoemission spectroscopy, and total yield spectroscopy. Clean and ordered 1x1 surfaces are prepared by nitrogen ion sputtering and annealing.@footnote 1@ The electron affinity, @chi@, is found equal to 3.3±0.2 eV and 1.9±0.2 eV for GaN and AlN surfaces, respectively, in agreement with previous results.@footnote 2,3@ The deposition of Cs reduces @chi@(AlN) by 2.6±0.3 eV, leading to true negative electron affinity (NEA), i.e. the vacuum level (E@sub vac@) is below the conduction band minimum (E@sub c@) at the surface. With the assist of a 1.2 eV initial downward band bending, effective NEA, i.e E@sub vac@ below the bulk E@sub c@, is achieved on p-GaN following the sequential adsorption of oxygen and deposition of cesium, which lowers @chi@(GaN) by 2.7±0.3 eV. The total yield, defined as the ratio of the total emitted current to the incident current, is strongly affected by the direction of band bending near the surface. For Cs/AlN, the upward band bending limits the total yield which reaches a maximum of 8 for incident electron energies of 600~900 eV and then decreases rapidly because secondary electrons excited deep in the solid are pushed back to the bulk by the field of the depletion region. On the other hand, Cs/GaN gives a maximum yield of 20 at higher incident electron energy (1200~1400 eV). This maximum is preserved up to much higher incident energy because the field of depletion region helps secondary electrons escape from the NEA solid.@FootnoteText@@footnote 1@ C.I. Wu, A. Kahn, E.S. Hellman and D.N.E. Buchanan, Appl. Phys. Lett., 73, 1346 (1998). @footnote 2@C.I. Wu and A. Kahn, Appl. Phys. Lett, 74, 546 (1999) @footnote 3@C.I. Wu and A. Kahn, J. Vac. Sci. Technol. B16, 2218 (1998) .