Depletion region

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

Accumulation and Depletion Layer Thicknesses in Organic Field Effect Transistors

Abstract: We present a simple but powerful method to determine the thicknesses of the accumulation and depletion layers and the distribution curve of injected carriers in organic field effect transistors. The conductivity of organic semiconductors in thin film transistors was measured in situ and continuously with a bottom contact configuration, as a function of film thickness at various gate voltages. Using this method, the thicknesses of the accumulation and depletion layers of pentacene were determined to be 0.9 nm (VG=-15 V) and 5 nm (VG=15 V), respectively.

The Copper Oxide Rectifier

Abstract: It is shown that the conductivity in the ohmic part of the cuprous oxide layer can be explained with the usual band picture of semiconductors only by assuming the presence of some donor-type impurities in addition to the usual acceptor type. The energy difference between the acceptors and the filled band is 0.3 electron volt, and the total number of impurity atoms is about ${10}^{14}$ to ${10}^{16}$ per ${\mathrm{cm}}^{3}$, the number of donors being less than but of the same order as the number of acceptors. Applying the Schottky theory of the space charge exhaustion layer, one finds from the dependence of capacity of the rectifier on bias voltage that the density of ion charge in the rectifying layer is of the same order of magnitude as the difference between the donors and acceptors found from the conductivity, thus furnishing a check for the theory. The field at the copper-cuprous oxide interface calculated from the space charge is about 2\ifmmode\times\else\texttimes\fi{}${10}^{4}$ volts/cm; the height of the potential at the surface as compared with the oxide interior is about 0.5 volt; and the thickness of the space charge layer about 5.0\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}5}$ cm. The diffusion equation for flow of current through this space charge region can be integrated to give the current in terms of the field at the interface and the applied potential across the space charge layer. Two currents are involved, one from the semiconductor to the metal (${I}_{s}$) and one from the metal to the semiconductor (${I}_{m}$) which is similar to a thermionic emission current into the semiconductor. The net current is, of course, $I={I}_{m}\ensuremath{-}{I}_{s}$. One can get this "emission" current (${I}_{m}$) by dividing the true current by the factor $1\ensuremath{-}\mathrm{exp}(\ensuremath{-}\frac{e{V}_{a}}{\mathrm{kT}})$, where ${V}_{a}$ is the applied potential. This emission current depends on the absolute temperature and on the field at the copper-cuprous oxide interface. At high fields the logarithm of the current is proportional to the square root of the field, and at low fields the current decreases more rapidly indicating a patchy surface having small areas of low potential maximum from which all the emission comes when the field is large. This effective potential maximum measured from the Fermi level in the copper is about 0.5 ev, and the fraction of the total area effective ranges from ${10}^{\ensuremath{-}2}$ to ${10}^{\ensuremath{-}5}$ depending on how the rectifier was made. This last factor---the fraction of the area having this low potential maximum---is by far the most important variable, resulting in low reverse currents when the fraction is small and large reverse currents when the fraction is large.

Threshold Voltage Shifts in Organic Thin‐Film Transistors Due to Self‐Assembled Monolayers at the Dielectric Surface

Abstract: Recently, it has been shown by several groups that the electrical characteristics of organic thin-film transistors (OTFTs) can be significantly influenced by depositing self-assembled monolayers (SAMs) at the organic semiconductor/dielectric interface. In this work, the effect of such SAMs on the transfer characteristics and especially on the threshold voltage of OTFTs is investigated by means of two-dimensional drift-diffusion simulations. The impact of the SAM is modeled either by a permanent space charge layer that can result from chemical reactions with the active material, or by a dipole layer representing an array of ordered dipolar molecules. It is demonstrated that, in both model cases, the presence of the SAM significantly changes the transfer characteristics. In particular, it gives rise to a modified, effective gate voltage V eff that results in a rigid shift of the threshold voltage, ΔV th , relative to a SAM-free OTFT. The achievable amount of threshold voltage shift, however, strongly depends on the actual role of the SAM. While for the investigated device dimensions, an organic SAM acting as a dipole layer can realistically shift the threshold voltage only by a few volts, the changes in the threshold voltage can be more than an order of magnitude larger when the SAM leads to charges at the interface. Based on the analysis of the different cases, a route to experimentally discriminate between SAM-induced space charges and interface dipoles is proposed. The developed model allows for qualitative description of the behavior of organic transistors containing reactive interfacial layers; when incorporating rechargeable carrier trap states and a carrier density-dependent mobility, even a quantitative agreement between theory and recent experiments can be achieved.

MISFET semiconductor device having relative impurity concentration levels between layers

Abstract: A semiconductor device having a MISFET with an EV source/drain structure has a gate electrode formed on part of a first p-type semiconductor layer via a gate insulating film. A second n + -type semiconductor layer is formed in the prospective source and drain regions of the first semiconductor layer via the gate electrode, and a third n − -type semiconductor layer is formed on the second semiconductor layer. Each of source and drain regions is formed from the second and third semiconductor layers. The upper edge of the source/drain regions is formed above the boundary between the first semiconductor layer and the gate insulating film. In an ON state, part of a depletion layer in the drain region is formed in the third semiconductor layer, and part of a depletion layer in the source region is formed in the second semiconductor layer.

Transport mechanisms in ZnO/CdS/CuInSe2 solar cells

Abstract: The transport mechanisms in ZnO/CdS/CuInSe2 solar cells prepared by ARCO (now Siemens) Solar Inc. have been analyzed by measurements of current versus voltage at different temperatures in the dark, short‐circuit current versus open‐circuit voltage at different temperatures in the light, spectral response of quantum efficiency, and junction capacitance. In the dark, recombination in the depletion region and/or thermally assisted tunneling are the dominant transport mechanisms. The observation of a smaller open‐circuit voltage than would be predicted from the dark transport parameters is the result of a small change in the transport parameters under illumination, probably without a change in transport mechanism.