Depletion region

About: Depletion region is a research topic. Over the lifetime, 9393 publications have been published within this topic receiving 145633 citations.

Size dependence of the ferroelectric transition of small BaTiO3 particles: Effect of depolarization.

Abstract: A theory has been developed to examine the depolarization effect on the ferroelectric transition of small ${\mathrm{BaTiO}}_{3}$ particles. To reduce the depolarization energy, a crystal would break up into domains of different polarization. In this study, we consider cubic particles with alternating domains separated by 180\ifmmode^\circ\else\textdegree\fi{} domain walls. The depolarization energy and the domain-wall energy were incorporated into the Landau-Ginzburg free-energy density. Assuming a hyperbolic tangent polarization profile across the domain wall, the domain-wall energy \ensuremath{\gamma} and the domain-wall half thickness \ensuremath{\xi} can be obtained by minimizing \ensuremath{\gamma} with respect to \ensuremath{\xi}. To account for ${\mathrm{BaTiO}}_{3}$ not being a perfect insulator, a Schottky space charge layer beneath the particle surface that shields the interior of the crystal from the depolarization field was considered. The equilibrium polarization P and domain width D can be obtained by minimizing the total free-energy density with respect to both P and D. The results of the calculations show that the ferroelectric transition temperature of small particles can be substantially lower than that of the bulk transition temperature as a result of the depolarization effect. Consequently, at a temperature below the bulk transition temperature, the dielectric constant \ensuremath{\epsilon} can peak at a certain cube size L. These results agree with the existing experimental observations. Finally, the theory can also be applied to other ferroelectric materials such as ${\mathrm{KH}}_{2}$${\mathrm{PO}}_{4}$ or ${\mathrm{PbTiO}}_{3}$.

Mechanism of carrier transport in highly efficient solar cells having indium tin oxide/Si junctions

Abstract: The carrier transport mechanism of the Si solar cells having n‐Si/indium tin oxide (ITO) junctions has been studied by use of the current‐voltage and capacitance‐voltage measurements and x‐ray photoelectron spectroscopy. An 11‐A‐thick nonstoichiometric Si oxide layer is formed when ITO is deposited by spray pyrolysis on a Si electrode etched with hydrofluoric acid. In this case, the tunneling probability of majority carriers through the oxide layer is high, and the thermionic emission current over the energy barrier in Si takes a dominant part of the dark current. On the other hand, for a Si electrode where a Si oxide layer is intentionally interposed between ITO and Si, the thermionic emission current is suppressed, and trap‐assisted multistep tunneling through the depletion layer becomes dominant. By making a mat‐structure treatment on the Si surface, a solar energy conversion efficiency of 13% and the photocurrent density of 42.5 mA cm−2 were attained under AM 1 100 mW cm−2 illumination.

Effect of surface fields on the breakdown voltage of planar silicon p-n junctions

Abstract: The effect of surface fields on the breakdown voltage of planar silicon diodes is studied experimentally and theoretically. It is shown that the breakdown voltage can be modulated over a very wide range by the application of an external surface field and that it tends to saturation at a maximum and at a minimum value as the gate voltage is varied in such a way as to deplete the lowly doped and highly doped sides of the junction, respectively. Both the high- and the low-voltage saturation of the breakdown voltage appear to be due to the formation of field-induced junctions which prevent further variation in the shape of the depletion region, and hence the breakdown voltage. Between these two extremes, the breakdown voltage is found to be approximately given by BV=mV_{G} +constant, where V G is the gate-to-substrate potential. The slope m approaches unity for low substrate impurity concentrations and for small oxide thicknesses. Numerical solutions of the two-dimensional potential distribution problem give results which are in general agreement with the above experimental observations.

Vertical one-transistor floating-body DRAM cell in bulk CMOS process with electrically isolated charge storage region

Abstract: A one-transistor, floating-body (1T/FB) dynamic random access memory (DRAM) cell is provided that includes a field-effect transistor fabricated using a process compatible with a standard CMOS process. The field-effect transistor includes a source region and a drain region of a first conductivity type and a floating body region of a second conductivity type, opposite the first conductivity type, located between the source region and the drain region. A buried region of the first conductivity type is located under the source region, drain region and floating body region. The buried region helps to form a depletion region, which is located between the buried region and the source region, the drain region and the floating body region. The floating body region is thereby isolated by the depletion region. A bias voltage can be applied to the buried region, thereby controlling leakage currents in the 1T/FB DRAM cell.