Electric Currents at Semiconductor Surfaces from the Perspective of Drift-Diffusion Equations

Surface sensitive electric current measurements are important experimental tools poorly corroborated by theoretical models. We show that the drift-diffusion equations offer a framework for a consistent description of such experiments. The current flow is calculated as a perturbation of an equilibrium solution depicting the space charge layer. We investigate the accumulation and inversion layers in great detail. Relying on numerical findings, we identify the proper length parameter, the relationship of which with the length of the space charge layer is not simple. If the length parameter is large enough, long-ranged modes dominate the Green's function of the current equation, leading to two-dimensional currents. In addition, we demonstrate that the surface behavior of the currents is ruled by only a few parameters. This explains the fact that simplistic conductivity models have proven effective but makes reconstructions of conductance profiles from surface currents rather questionable.Comment: 11 pages, 3 figures; some overlap with arXiv:1605.0268

Appearance of effective surface conductivity - an experimental and analytic study

Surface conductance measurements on p-type doped germanium show a small but systematic change to the surface conductivity at different length scales. This effect is independent of the structure of the surface states. We interpret this phenomenon as a manifestation of conductivity changes beneath the surface. This hypothesis is confirmed by an analysis of the classical current flow equation. We derive an integral formula for calculating of the effective surface conductivity as a function of the distance from a point source. Furthermore we derive asymptotic values of the surface conductivity at small and large distances. The actual surface conductivity can only be sampled close to the current source. At large distances, the conductivity measured on the surface corresponds to the bulk value.Comment: 11 pages, 8 figure

The benefits of vitamin D3 supplementation for menopausal women - literature review

Witamina D to potoczna nazwa cholekalcyferolu i ergokalcyferolu. Występuje w postaci nieaktywnej, ale w wyniku hydroksylacji w pozycji 1 lub 25 staje się witaminą aktywną. Cholekalcyferol paszy z nieaktywnej formy pod wydanie UV w ciało ciało, natomiast ergosterol jest dostarczany do organizmu z pożywienia roślinnego. Witamina D ma znaczący wpływ na zdrowie kobiet po menopauzie. Poziom estrogenu spada u kobiety w okresie menopauzy. Ma to konsekwencje m.in. ubytki wapnia. To jest powód, dla którego kobiety w tym wieku znajduje się w grupie ryzyka zachorowania na osteoporozę. Witamina D pomaga w przyswajaniu wapnia i fosforu. Te minerały pełnią wolę wolę w okresie menopauzy.Kobiety w tej grupie wiekowej przyjmować od 1000 do 1500 mg dziennie. Nie zaleca się nadmiernego spożycia, przekroczenie normy nie przynosi lepszych efektów. Mimo to wykrycie niedoboru witaminy D u kobiet po menopauzie i rozpoczęcie leczenia pozytywnie wpływ na ich stan zdrowia. [1

Fermi level pinning at the Ge(001) surface - A case for non-standard explanation

To explore the origin of the Fermi level pinning in germanium we investigate the Ge(001) and Ge(001):H surfaces. The absence of relevant surface states in the case of Ge(001):H should unpin the surface Fermi level. This is not observed. For samples with donors as majority dopants the surface Fermi level appears close to the top of the valence band regardless of the surface structure. Surprisingly, for the passivated surface it is located below the top of the valence band allowing scanning tunneling microscopy imaging within the band gap. We argue that the well known electronic mechanism behind band bending does not apply and a more complicated scenario involving ionic degrees of freedom is therefore necessary. Experimental techniques involve four point probe electric current measurements, scanning tunneling microscopy and spectroscopy.Comment: 5 pages, 4 figure

Effect of a skin-deep surface zone on formation of two-dimensional electron gas at a semiconductor surface

Two dimensional electron gases (2DEGs) at surfaces and interfaces of semiconductors are described straightforwardly with a 1D self-consistent Poisson-Schr\"{o}dinger scheme. However, their band energies have not been modeled correctly in this way. Using angle-resolved photoelectron spectroscopy we study the band structures of 2DEGs formed at sulfur-passivated surfaces of InAs(001) as a model system. Electronic properties of these surfaces are tuned by changing the S coverage, while keeping a high-quality interface, free of defects and with a constant doping density. In contrast to earlier studies we show that the Poisson-Schr\"{o}dinger scheme predicts the 2DEG bands energies correctly but it is indispensable to take into account the existence of the physical surface. The surface substantially influences the band energies beyond simple electrostatics, by setting nontrivial boundary conditions for 2DEG wavefunctions.Comment: 9 pages, 7 figures, 2 table