Observation of the resonance tunneling in field emission structures

Theoretical and experimental investigations of electron field emission from silicon-based resonance-tunneling layered structures have been performed. Numerical simulation of resonant and nonresonant field emission in ${\mathrm{Si-SiO}}_{\mathrm{2}}-{\mathrm{Si}}^{\mathrm{*}}-{\mathrm{SiO}}_{\mathrm{2}}$ multilayer cathodes (MLCs) with quantum well (QWs) which takes into account the tunneling process of electrons from the three-dimensional electron density state of the emitter conductive band has been carried out. The influence of the external electric field, temperature, MLC parameters and emitter doping on the resonant characteristics of the current was analyzed. Computer simulation has shown that the peak current density of MLCs with optimal thin barriers and sufficiently wide QW layers at a resonant value of the electric field can sometimes exceed the current density of conventional cathodes. If the width of the QW is increased, the number of current resonant maxima (CRM) is multiplied. The CRM is shifted towards the lower electric field values and become more narrow if both the QW and the potential barrier widths are increased. With temperature reduction the CRM becomes contrasted due to an increase in the electron impulse relaxation time and redistribution of the electron state density in the emitter conduction band. Experimental multilayer structures with ${\mathrm{Si}}^{\mathrm{*}}$ δ-doped layer ${\mathrm{Si-SiO}}_{\mathrm{2}}-{\mathrm{Si}}^{\mathrm{*}}-{\mathrm{SiO}}_{\mathrm{2}}$ have been formed on silicon using low pressure chemical vapor deposition of ultrathin ${\mathrm{SiO}}_{\mathrm{2}}$ and ${\mathrm{Si}}^{\mathrm{*}}$ films. In some cases the first ultrathin ${\mathrm{SiO}}_{\mathrm{2}}$ layer was grown on silicon with thermal oxidation. The multilayer structures were formed both on flat silicon wafers and on silicon tip arrays. Measurements of electron field emission into vacuum were performed in a diode (cathode-anode) system. The resonant peaks of current density from MLCs have been observed experimentally for the first time. The value of these peaks is more than two times of that of the background curves. A comparison of experimental and theoretical results has been performed to evaluate the fundamental parameters of the field emission resonance process.