Low-field electron emission of Si microtip arrays produced by laser beam evaporation

Results are reported on low-field electron emission (FEE) from periodical arrays of microtips produced by a laser-assisted evaporation of single-crystal Si wafers in a vacuum. The best samples showed the emission at threshold fields of as low as 4–5 V/μm for an n-type Si substrate and of 1–2 V/μm for a p-doped Si substrate as measured with the flat screen technique. The emission was stable upon cyclic variations of the electric field. Microscopic studies using a special scanning tunneling microscopy device show that: (i) the typical radius of the tip apex is about 1 μm, (ii) there are well-conducting as well as poorly conducting regions on the tip surface, (iii) the emission originates from the well-conducting regions, and (iv) as a rule, the emitting sites are submicron in size and are associated with some features of the tip microrelief, such as folds or valleys, but the FEE maxima do not correlate with relief peaks (protrusions). The experimental data allow us to explain the FEE from the tip arrays by a geometric field enhancement on narrow conducting channels in the tip body.