MODEL-CALCULATIONS OF INTERNAL FIELD-EMISSION AND J-V CHARACTERISTICSOF A COMPOSITE N-SI AND N-DIAMOND COLD-CATHODE SOURCE

A model to describe internal field emission through the interface betw een highly n-doped Si and nitrogen (N)-doped diamond is presented. We describe the roughness on the Si surface as a collection of sharp, sph erically pointed Si asperities embedded in the diamond film. These ''t ips'' provide enhancement of the applied electric held, which, in conj unction with the high N doping of diamond, results in the formation of a Schottky barrier which allows for tunneling or internal field emiss ion from the Si into the conduction band of diamond. This enhanced ele ctric held is also sufficient to induce valence band tunneling from th e Si into the diamond conduction band. In our model limitations on the held mediated transport of holes from the n-doped Si/diamond interfac e to the cathode base leads to charging of the Si asperities. This cha rge accumulation results in band bending in Si and a significant reduc tion in the valence band current. The calculated J-V characteristics f or the internal field emission lead to nonlinear behavior when plotted in Fowler-Nordheim coordinates. This is a consequence of the Limitati on of the conduction band current due to density of states effects at high fields in addition to the suppression of the valence band current . The calculated results are in qualitative agreement with recent fiel d emission studies of Okano et al. [K. Okano, S. Koizumi, S. Ravi, P. Silva, and G. A. J. Amaratunga, Nature 381, 140 (1996)] for a composit e n-Si and N-diamond cold cathode source. A plausible geometric argume nt suggests that there is also reasonable quantitative agreement. (C) 1998 American Vacuum Society.[S0734-211X(98)02802-9].