Analysis of Measured I(V) Relations for Electron Emission from Insulating Diamond Films on Various SI Substrates
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ABSTRACT In this work, we shall analyze the performance of a geometrical interface roughness model to estimate current from p-type silicon into insulating diamond and compare the performance of that model to experimental data. A minimum number of adjustable parameters are invoked. While the model qualitatively accounts for trends in the experimental data, in particular, the shift from negative to positive slope on a Fowler Nordheim plot of the I(V) data, it does so at the expense of demanding ellipsoid parameters that appear to be unreasonable. We therefore conclude that a simple geometrical field enhancement model of interface roughness is insufficient to account for the current observed, and thus the theory must be augmented by a more comprehensive electron transport model at the interface.
INTRODUCTION Field emission from microfabricated diamond structures hold promise for high power applications, in which the operating environment is known to be deleterious to cold-cathode candidates. In presence of high energy back streaming ions and background pressures on the 2 order of 10-' Torr, current densities on the order of 10 A/cm are needed (and one to two orders higher for exotic and next generation amplifiers. For these power tube applications, uniformity of electron emission is critical, and the robustness of any cold cathode candidate is essential. Diamond is an interesting candidate due to its potentially low voltage operation, but the basic emission mechanisms and ultimate capabilities are poorly understood. Emission measurements from insulating diamond on p- and n-doped Si substrates suggest that the substrate-diamond interface plays a dominant role in the electron emission of a diamond film [I]. In particular, Fowler Nordheim plots of the current-voltage relationship for diamond films on p-doped silicon substrates display convexity at low currents. The experimental data was taken from diamond samples grown in a microwave plasma-assisted CVD setup. Repeatable and characteristic I(V) behavior was obtained from the samples. The findings of a heuristic model of internal field emission based on ad hoc modifications to a WKB analysis of the potential at the substrate-diamond interface [2] observed a similar behavior for a semiconductor-on-metal model. On the assumption that the between diamond - silicon interface accounts for the behavior of the experimental results, we seek to ascertain if a simple geometrical internal field emission model may account for the qualitative features of the data, and if so, what parameters are required.
EXPERIMENTAL RESULTS The insulating diamond films in a microwave plasma-assisted CVD setup [3] using a hydrogen plasma with 0.8% methane, a substrate temperature of 650-700 'C, and a total pressure of 35 mbar. Field emission topography mapping (FETM) of the surface revealed that the grain size of the film was approximately 2 pAm. Two of the samples reported in Ref. [1] are the focus of our
603 Mat. Res. Soc. Symp. Proc. Vol. 558 © 2000 Materials Research Society
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