Electron emission and NEA from differently terminated, doped and oriented diamond surfaces

We investigated band bending, electron affinity and work function of differently terminated, doped and oriented diamond surfaces. Electron emission from energy levels below the conduction band minimum up to the vacuum level E-vac permitted us to measure quantitatively the negative electron affinity (NEA). All the H-terminated surfaces present NEA with an upper limit of -0.2 eV for the nitrogen-doped and -1.0 eV for the boron-doped diamond crystals. The characteristic NEA peak of the ultraviolet photoelectron spectrum is observed only for the boron-doped diamond (100)-(2 x 1):H and (110)-(1 x 1):H surfaces. The high intensity NEA peak of boron-doped diamond seems to be due to the downward band bending together with the reduced work function because of hydrogen termination. For the nitrogen-doped diamond the work function behaves similarly but no NEA peak is observed because of the surface barrier formed by the high upward band bending. With the knowledge of the band structure we will discuss the possibility of using diamond as cold cathode material and outline an emission model for the different diamond surfaces. (C) 1999 Elsevier Science S.A. All rights reserved.