Mechanism of Highly Efficient Electron Emission from a Graphene/Oxide/Semiconductor Structure

Abstract

Highly efficient electron emission of 48.5% was demonstrated by a graphene/oxide/semiconductor (GOS) structure. The main factors contributing to this performance were investigated by analyzing the energy distributions of the emitted electrons and the current conduction mechanism through the oxide layer. The energy level of the lower tail of the electron energy distribution was 2.4−2.6 eV above the work function of the graphene electrode, indicating that the work function of the gate electrode does not affect the electron emission efficiency. In addition, Fowler−Nordheim (FN) tunneling was the dominant current conduction mechanism in the oxide layer when the GOS structure exhibited highly efficient electron emission. These findings indicate that the high electron transmittance of the graphene electrode and the pure FN tunneling current through the oxide layer were responsible for the highly efficient electron emission from the GOS structure. These results further indicate the possibility of experimentally evaluating the low-energy electron transmittance of graphene with various layer numbers by analyzing the electron emission efficiency of the GOS structure. The maximum electron emission efficiency of the GOS structure was predicted to be approximately 70.3% using the high electron transmittance of single-layer graphene determined in this study.

Efficient and Dense Electron Emission from a SiO2 Tunneling Diode with Low Poisoning Sensitivity

“…Cold electron sources that can be microfabricated on chips have been another pursuit for more than 50 years, as they can work at room temperature and facilitate scaling down and integration of EB-based devices and instruments. Field emission sources have been intensively studied for this purpose and exhibit several advantages, including efficient and dense electron emission. , In addition to field emission sources, tunneling electron sources (TESs) based on the emission of hot electrons generated in tunneling junctions are another long-term-studied and promising candidate for such cold electron sources. − In contrast to the prerequisite for UHV for field emission sources, tunneling emission has been demonstrated to be independent of pressure from 10 –6 to 1 Pa, as it is governed by the electric field inside the insulator and planar electron-emitting surfaces with low air reactivity are employed. However, TESs have in common the requirement of a diode-type structure to apply a voltage to the tunneling junction for hot electron generation and the issue that hot electrons are mostly thermalized before emission due to unavoidable inelastic scattering .…”

“…First, hot electrons in our device encounter less restriction in space than those in a conventional TES. A conventional TES generally employs vertically stacked metal (or semiconductor)–insulator–metal (or semiconductor) tunneling junctions, − where hot electrons are generated in the buried insulator layer and have to be transported across the above metal (or semiconductor) layer before emission (Figure S1). Hot electrons with sufficient energy for emission in the insulator mostly cannot be finally emitted into vacuum, as they are thermalized due to inelastic scattering during their transport across the above metal (or semiconductor) layer, which works as a blocking layer, giving strong spatial restriction on electron emission.…”

Low-Field Electron Emission Capability of Thin Films on Flat Silicon Substrates: Experiments with Mo and General Model for Refractory Metals and Carbon

“…However, LMF emissivity of nanogranular metal thin films manifested without any additional energizing had been previously reported, e.g., by Purohit et al [86,87]. Moreover, several of the early experiments with MOS sandwich films discussed above employed relatively high magnitudes of extracting electric field applied to emitting structure surface: 5 kV/10 mm in [41], 1000 V/5 mm in [26], etc. This is comparable with threshold field values for the best samples tested in the present work, and the emission, observed in those experiments, could have been caused, at least partially, by the direct action of the applied field, not by the feeding current.…”

“…Later, with refined technologies, the properties of MIM/MOS cathodes were significantly improved [22,23], while the emission mechanism apparently came into agreement with the original concept [15]. The most recent progress was related to the idea of using graphene (G) films as top electrodes [24][25][26]; Murakami et al reported on the achievement of emission efficiency up to ~50% and current densities >100 mA/cm 2 with the GOS structures [26].…”

“…Those smooth-surface structures had much in common with the structures discussed above, but in our experiments, no energizing current was passed either through or along the emitting structure. Nonetheless, cold electron emission was induced by an electric field with a macroscopic magnitude as low as 1 V/µm or less, i.e., of the same order as the field employed for extraction of emitted electrons in the experiments where the highest emission efficiency values were obtained with planar MOS or GOS sandwich structures (5 kV/10 mm in [41], 1 kV/5 mm in [26]). Emissivity of the tested films emerged or improved after an electrothermal forming treatment.…”