Effect of dipole structures on field emission of wide-gap semiconductor emitters

It is shown that dipole structures placed in a thin (less than 1 nm) near-surface layer of a high-resistivity field emitter produce small domains on the emitting surface in which the electric field may exceed 10$^8$ V/cm. In these domains, the emitter surface potential is positive, providing effective electron transport from inside the emitter to the emission boundary. Optimal dipole orientations ensuring maximal electric fields at the surface are found. When the surface density of dipoles localized in the near-surface layer is on the order of 10$^6$ cm$^{-2}$, one can expect an emitter-averaged emission current density of higher than 1 A/cm$^2$. The dipole structures in the near-surface layer may persist owing to incorporated impurity molecules having a dipole moment or result from a random combination of positively charged ionized impurities and electrons captured by deep traps. Trap charging/discharging asymmetry accounts for the hysteresis of the emission I–V characteristics.