A model for internal photoemission at high-k oxide/silicon energy barriers

A model has been developed to describe the emission of electrons from silicon across the oxide energy barrier of metal-oxide-silicon structures. An optical absorption coefficient, exclusively describing the transmission of electrons which are emitted across the barrier, is split from the corresponding experimental quantity for the entire absorption range. This makes it possible to approximate the photo yield in terms of absorption coefficients and density of states without need for explicitly calculated matrix elements of optical transitions. Using this method, theoretical emission yield curves are found in good agreement with measured data. An important conclusion from this work is that values of oxide energy barrier heights should be extracted from different features of the yield data than most often done in the literature. This replaces a commonly used practice for determining the barrier heights, which is shown to be based on optical bulk properties of the silicon crystal

Télévision, moyens d’information et comportement électoral

La campagne électorale qui a précédé les consultations de l'automne 1962 et l'analyse des résultats qui les ont suivies ont fourni à la presse l'occasion d'un grand nombre d'articles sur l'effet des moyens d'information, et en particulier de la télévision (...)

Photoemission yield and the electron escape depth determination in metal-oxide-semiconductor structures on N+-type and P+-type silicon substrates

This article gives a quantitative analysis of electron photoemission yield from N+-type and P+-type substrates of MOS structures. Based on this analysis, a method is presented to estimate both the scattering length, l, of electrons in the image force potential well and of photoelectron escape depth, x(esc), from the semiconductor substrate. This method was used to estimate the scattering length and the escape depth from the substrates of Al-SiO2-Si (N+-type and P+-type) structures. It was found that for N+-type substrate structures the scattering in the image force potential well has a dominating influence on the photoemission yield while for P+-type substrate structures both the scattering in the image force potential well and the photoemission from the subsurface regions of the photoemitter play important roles. It was found that the scattering length in the image force potential well was equal to l = 6.7-6.9 nm for structures on both N+ and P+ substrates, produced in the same processing conditions. For structures on P+ substrates, the escape depth was found to be equal to x(esc) = 8-9 nm. The scattering length, l, determined in this study is considerably larger than the one reported previously (l = 3.4 nm) for similar MOS structures. The escape depth x(esc) determined in this study is also considerably larger than the escape depth determined previously (x(esc) = 1.2-2.5 nm) for the external photoemission from uncovered silicon surfaces into vacuum

Effect of oxide traps on channel transport characteristics in graphene field effect transistors

A semiempirical model describing the influence of interface states on characteristics of gate capacitance and drain resistance versus gate voltage of top gated graphene field effect transistors is presented. By fitting our model to measurements of capacitance–voltage characteristics and relating the applied gate voltage to the Fermi level position, the interface state density is found. Knowing the interface state density allows us to fit our model to measured drain resistance–gate voltage characteristics. The extracted values of mobility and residual charge carrier concentration are compared with corresponding results from a commonly accepted model which neglects the effect of interface states. The authors show that mobility and residual charge carrier concentration differ significantly, if interface states are neglected. Furthermore, our approach allows us to investigate in detail how uncertainties in material parameters like the Fermi velocity and contact resistance influence the extracted values of interface state density, mobility, and residual charge carrier concentration

Analysis of electron capture at oxide traps by electric field injection

Electron injection into oxide traps of metal/high-k oxide/interlayer/silicon structures is investigated by modeling. We demonstrate the influence on flat-band voltage by the sharpness of the interlayer/silicon interface and by the properties of traps in the oxide. Since charge carrier injection in this kind of structures may take place by two different processes simultaneously, excluding one or the other in the interpretation of data may lead to considerable erroneous results in extracted values of capture cross sections

flexibility at a glycosidic linkage revealed by molecular dynamics stochastic modeling and 13c nmr spin relaxation conformational preferences of α l rhap α 1 2 α l rhap ome in water and dimethyl sulfoxide solutions

Coupling between global reorientation and local motion is essential for reproducing NMR relaxation parameters of a flexible molecule

Energy concepts involved in MOS characterization, Journal of Telecommunications and Information Technology, 2007, nr 2

Starting from a quantum statistical reasoning, it is demonstrated that entropy properties of silicon/silicon dioxide interface electron traps may have a strong influence on measured distributions of interface states, depending on measurement method used. For methods, where the Fermi-level is used as a probe to define an energy position, the scale is based on free energy. On the other hand, methods based on thermal activation of electrons give the distribution on an enthalpy scale. It is shown that measured interface state distributions are influenced by the distribution of entropy, and that common features of measured energy distributions may be influenced by entropy variations. These results are used to interpret experimental data on the energy distribution of electron capture cross sections with an exponential increase followed by a more or less constant value as the energy distance of the traps from the conduction band edge increases. Such a relation is shown to be consistent with a situation where the emission and capture processes of electrons obey the Meyer-Neldel rule

Electron Transport across Vertical Silicon/MoS2/Graphene Heterostructures: Towards Efficient Emitter Diodes for Graphene Base Hot Electron Transistors

Heterostructures comprising silicon, molybdenum disulfide (MoS2), and graphene are investigated with respect to the vertical current conduction mechanism. The measured current-voltage (I-V) characteristics exhibit temperature-dependent asymmetric current, indicating thermally activated charge carrier transport. The data are compared and fitted to a current transport model that confirms thermionic emission as the responsible transport mechanism across devices. Theoretical calculations in combination with the experimental data suggest that the heterojunction barrier from Si to MoS2 is linearly temperature-dependent for T = 200-300 K with a positive temperature coefficient. The temperature dependence may be attributed to a change in band gap difference between Si and MoS2, strain at the Si/MoS2 interface, or different electron effective masses in Si and MoS2, leading to a possible entropy change stemming from variation in density of states as electrons move from Si to MoS2. The low barrier formed between Si and MoS2 and the resultant thermionic emission demonstrated here make the present devices potential candidates as the emitter diode of graphene base hot electron transistors for future high-speed electronics. Copyright © 2020 American Chemical Society