V. G. Litovchenko

Quantum-size resonance tunneling in the field emission phenomenon

Theoretical analyses have been performed of the quantum-size (QS) resonance tunneling in the field-emission (FE) phenomenon for different models of the emitting structures. Such experimentally observed peculiarities have been considered as the enhancement of the FE current, the deviation from the Fowler-Nordheim law, the appearance of sharp current peaks, and a negative resistance. Different types of FE cathodes with QS structures (quantized layers, wires, or dots) have been studied experimentally. Resonance current peaks have been observed, from which the values of the energy-level splitting can be estimated.

Field emission from structures with quantum wells

Computer simulation studies of the properties of some novel types of field emitters have been carried out in the framework of the theory of quantum disc effects. The following cases have been analyzed in detail. (1) Emission from the field surface states (SS) exhibiting both discrete and continuous energy spectra. This case resembles the known effect of the work‐function deterioration ΔW∼(Ec−ESS), yet, here, prior to the emission into vacuum, the SS electrons must be excited the conductivity band via the Pool–Frenkel mechanism: ne≂C exp(aEs1/2/kT), or some other. (2) Emission from the δ‐doped structures via the internal field ionization of filled states, deposited near to surface in semiconductor or in super‐thin insulator layer. (3) Emission from the two‐dimensional (2D) quantum well (QW) surface space charge regions. In this case, the bottom of a subsurface c band is shifted by the quantization value E=Ec−Ei with Ei=(ℏ2/2m*)1/3 [3/2πeEs(i+3/4)]2/3∼Es2/3. Here Es=4π/2eNs is the strength of the surface el...

Formation of conducting nanochannels in diamond-like carbon films

A sharp increase of the emission current at high electric fields and a decrease of the threshold voltage after pre-breakdown conditioning of diamond-like carbon (DLC) films have been measured. This effect was observed for DLC-coated silicon tips and GaAs wedges. During electron field emission (EFE) at high electric fields the energy barriers caused by an sp3 phase between sp2 inclusions can be broken, resulting in the formation of conducting nanochannels between the semiconductor–DLC interface and the surface of the DLC film. At high current densities and the resulting local heating, the diamond-like sp3 phase transforms into a conducting graphite-like sp2 phase. As a result an electrical conducting nanostructured channel is formed in the DLC film. The diameter of the conducting nanochannel was estimated from the reduced threshold voltage after pre-breakdown conditioning to be in the range of 5–25 nm. The presence of this nanochannel in an insulating matrix leads to a local enhancement of the electric field and a reduced threshold voltage for EFE. Based on the observed features an efficient method of conducting nanochannel matrix formation in flat DLC films for improved EFE efficiency is proposed. It mainly uses a silicon tip array as an upper electrode in contact with the DLC film. The formation of nanochannels starts at the interface between the tips and the DLC film. This opens new possibilities of aligned and high-density conducting channel formation.

Observation of the resonance tunneling in field emission structures

The theoretical and experimental investigations of electron field emission from silicon-based resonance-tunneling layered structures have been performed. The simulation of emission processes in multilayer cathodes (MLC) with quantum well (QW) have been fulfilled.

Evidence of satellite valley position in GaN by photoexcited field emission spectroscopy

GaN field emitter rods with nanometer diameter were fabricated by photoelectrochemical etching on a n+-GaN substrate. Their electron field emission properties were investigated under ultraviolet (UV) illumination. The Fowler–Nordheim plots of the emission current show different slopes for nonilluminated and UV illuminated devices. A model based on the electron emission from valleys having different specific electron affinities is proposed to explain the experimental results. In the absence of illumination, the GaN rods are almost fully depleted and emission takes place only from the lower valley. Upon UV illumination and presence of a high electric field at the emitter tip, the upper valley of the conduction band appears to be occupied by electrons generated at the valence band. The energy difference between the lower and upper valleys was determined to be 1.15eV and is in good agreement with formerly published theoretical and measured values.

Gunn effect in field-emission phenomena

The peculiarities of electron field emission from nanostructured GaN surface have been investigated. The current–voltage characteristics of emission current in Fowler–Nordheim plot show two parts with different slopes. There are emission current oscillations in the changing slope region. As an explanation for the experimental results a model based on the electron-emission analysis from lower (Γ) valley, upper (U) valley, and electron transition between valleys due to heating in electric field has been proposed. The electron affinities for the emission from Γ and U valleys have been determined. The decreased affinities from there valleys have been estimated for quantization in nanostructured GaN.

Silicon tip arrays with nanocomposite film for electron field emission applications

Abstract An array of field emitting tips made on silicon with coating nanocomposite film was made by a laser direct-write process. The laser was used in air: a single laser pulses forms a single conical tip and moved to create an array. In this process, the silicon substrate (n-Si) is heated locally above its melting point by a pulse YAG:Nd3+ laser. At the working pressure (∼105 Pa), most of the Si particles are deposited back on the target and on to the tip. As a result, the conical surface had many protuberances, all covered with the nanocomposite film. This film consists of nanocrystalline silicon in an SiOxNy matrix. Several samples were stain etched, and porous silicon (PS) layers were formed on the conical surface. These PS layers form the composite structure that contains nanocrystalline silicon in a porous SiOxNyHz matrix. Fowler–Nordheim current–voltage characteristics were usually observed. Relatively high emission parameters: effective emission areas α=10−8 cm2, local field enhancement factors β=105 cm−1 have been obtained. A resonant tunneling phenomenon has been found on some samples. The resonant peaks have been observed. Due to the quantum-size effect, there are some energy levels in the quantum well region that cause an increased tunneling probability under certain values of the electric field.

Electrical and emission properties of nanocomposite SiOx(Si) and SiO2(Si) films

The electrical and emission properties of as deposited and annealed SiOx(Si) films have been investigated. The films with thicknesses of 10–100nm were obtained by thermal evaporation of silicon powder in vacuum (2.7–4.0)×10−3Pa on flat Si substrates and Si tip arrays. The atomic force microscopy investigations of the surface morphology indicated the presence of nanoprotrusions on surface of the initial SiOx(Si) films with height up to 20nm and curvature radius of the nanoprotrusions about 3–5nm. As a result of the thermal annealing, the film surface becomes more uniform and its morphology is characterized by nanoprotrusions with height in the range of 1–3nm. At low electric fields the I-V characteristics of dark current through the initial SiOx(Si) films correspond to Poole-Frenkel transport mechanism. The Fowler-Nordheim tunneling dominates at higher electric fields. As to annealed SiO2(Si) films, the modified Fowler-Nordheim electron tunneling through trapezoidal SiO2 barrier between silicon nanocluster...

Electron field emission from wide bandgap semiconductors under intervalley carrier redistribution

Electron field emission phenomena from semiconductors (and, in particular, wide band gap materials) are analyzed theoretically for the general case, i.e., by taking into consideration aspects that have not been considered earlier such as two (or more) valleys of the energy band structure, nondegenerated statistics for the free electrons, heating of conduction band electrons, intervalley carrier redistribution under applied electrical fields, size quantization of electron band spectra, and change in the field emission characteristics. Comparisons with experiments performed on the highly structured (micro- and nano) surfaces of the GaN wide bandgap semiconductor have been made. The influence of the above factors on the current-voltage Fowler–Nordheim characteristics was demonstrated by theory and experiment. From theoretical and experimental results the intervalley energy difference (ΔE) for GaN quantum-sized cathodes was estimated to be 0.8 eV, which is considerably less than that predicted for bulk semico...

Peculiarities of the electron field emission from quantum-size structures

Abstract The electron field emission from semiconductor based layered structures has been investigated. Among studied structures were silicon tips coated with ultra-thin DLC layer, multilayer structures Si–SiO 2 –Si ∗ –SiO 2 with delta-doped Si ∗ layer, nanocomposite layers SiO x N y (Si) with Si nanocrystals embedded in SiO x N y matrix, GaN layers and Si–SiGe heterostructures. All of them have such peculiarities of electron field emission as peaks on emission current–voltage characteristics and corresponding Fowler–Nordheim plots. A physical model is proposed for explanation of experimental results. All emitters have layer, cluster wire or dot with quantum-size restriction in it. As a result, the quantum well with splitted electron levels exists or appears at electric field. Additional mechanism of electron emission-resonance tunneling is realized at definite electric fields.