P1–24: Photo-assisted electron emission from MOS-type cathode based on nanocrystalline silicon

Abstract

Enhancement of electron emission by illumination of a metal-oxide-semiconductor (MOS)-type cathode based on nanocrystalline silicon has been studied using a He-Ne laser. Heavily doped p-type silicon was used as a substrate and the laser was irradiated on the gate with oblique incidence. The emission current was enhanced under illumination and quickly responded to on-off of the laser. In addition, the threshold voltage for the electron emission decreased. IntroductionA planar-type cold cathode with a metal-oxidesemiconductor (MOS) or a metal-insulator-metal (MIM) diode structure has big advantages for vacuum nanoelectronic applications, because the cathode operates at a low extraction voltage, and produces uniform and highly directional electron emission throughout the whole emission area, in contrast with a field emission cathode [1,2]. Furthermore, the cathode is insensitive to environment. However, measured values in emission efficiency were ordinarily less than 1 % and the energy of emitted electrons was relatively widely distributed due to electron energy losses and strong scattering of hot electrons in the tunneling barrier and the gate electrode in the diode [1,3]. In fact, a large number of electrons have been detected at energies lower than the original work function of the gate metal by cesiation [4]. The modified MOS-type cathodes were reported to have high efficiencies over 10 % [5,6]. In those cathodes, the oxide layer is replaced with oxidized films containing nano-or poly-crystalline silicon. We have also fabricated a MOS-type cathode based on nanocrystalline silicon prepared by pulsed laser ablation (nc-Si MOS cathode) and achieved an emission efficiency lager than 4 % [7]. However, the mechanism of such a high efficiency from the cathode using nanocrystalline structures is not well understood yet. Understanding the emission mechanism of the cathode based on nanocrystals is