Properties of plasma enhanced chemical vapor deposition diamond-like carbon films as field electron emitters prepared in different regimes

Abstract

The influence of the diamond-like carbon (DLC) films deposited in different conditions on electron field emission of silicon tips has been investigated. Arrays of square based pyramidal cathodes were fabricated in n-type Si(100) using wet etching in an acid mixture. Undoped and nitrogen doped DLC films were grown by plasma enhanced chemical vapor deposition method from CH4:H2 and CH4:H2:N2 gas mixtures, correspondingly. During nitrogen doped DLC films deposition the nitrogen content in gas mixture was varied from 0% to 45%. The DLC films thickness was changed in range from 10 to 100 nm. Refractive indexes of DLC films were lower for thinner layers. The effect of preparation conditions of the DLC films on their electron emission properties (work function, threshold voltage, etc.) has been studied. For comparison of the emission properties of the structures with DLC films deposited in different conditions the threshold (onset) voltages, field enhancement factors, effective emission areas, calculated from Fowler–Nordheim plots, have been used. It was confirmed that for DLC coatings the electron field emission was substantially increased in comparison with the emission from silicon tips without the coatings, although the nonmonotonous dependence of effective work function on the refractive index of DLC films has been observed. In this context, optimization experiments with respect to the minimal value of the effective work function, which in some cases was less than 1 eV, have been performed. It was found that for the structures with nitrogen doped DLC films the emission appears at lower voltages and the calculated effective work function is 0.1 eV less than for case of the best undoped DLC films. The obtained results can be used for the development of the high efficient field emission cathodes. The model for explanation of the experimental results is presented and the role of carbon–carbon, carbon–hydrogen, and carbon–nitrogen bonds is discussed.