Injection of charges

A light-emitting diode (LED) is a forward-biasedp—n junction in which the appHed bias enables the recombination of electrons and holes at the junction, resulting in the emission of photons. This type of light emission resulting from the injection of charged carriers is referred to as electroluminescence. A direct band gap semiconductor is optimal for efficient light emission and thus the majority of the compound semiconductors are potential candidates for efficient LEDs. 

The purpose of the n-type doped a-Si H layer is to prevent injection of charge from the substrate into the photoconductor. Thus it serves as a blocking layer. Injection of surface charge into the photoconductor is prevented by the surface... 

FETs can be viewed partly as capacitors, with the gate and semiconductor functioning as parallel-plate electrodes. As long as the semiconductor has accessible orbitals for the injection of charge and is sufficiently continuous, the gate-source voltage charges the capacitor. 

In many cases, local details are not important and an overall balance of generation and recombination, of extraction and injection of charge carriers gives the correct results for electrical and energy currents originating from a solar cell, as we know from extensive experience. 

The hole mobility /u-h in OCiCio-PPV is 5 x 10-11 m2/V s. The electron mobility /xe in PCBM is 2 x 10-7 m2/V s. However, the transport of separate charge carriers in an interpenetrating network may be different than the transport in the individual compounds. In Ref. [65] the transport and injection of charge carriers in OCiCio-PPV PCBM bulk-heterojunction diodes are investigated. 

Contact metamorphism takes place in small areas adjacent to a hot mass, like a chamber of molten rock. It can occur two ways, either through the heating of the surrounding rocks (thermal) or by a combination of heat and the injection of charged fluids from the igneous body (hydrothermal). Many ore deposits are formed hydrothermally. 

The electronic properties of carriers near the interface are also influenced by bulk traps in the nitride or other dielectric material. Trapping at interface states and in the bulk dielectric are differentiated by their respective time constants. The distinction between fast interface states and slow bulk states is well known in crystalline silicon. Similarly, the injection of charge from the a-Si H layer into the nitride has a range of time constants which can extend for hours at room temperature. 

Injection of charge from the CGL into the CTL must also be rapid and not subject to significant trapping. 

The problem of detailed modeling can be divided into three parts (1) What is the shape of the energy bands within the device, particularly close to the electrodes (2) What is the mechanism for injection of charges through any barriers which are formed at the interface (3) To what extent are the characteristics of the device determined by transport and recombination within the bulk of the polymer, rather than by injection at the interfaces ... 

These observations along with the independence of the EL spikes on the applied voltage polarity13 suggests that the EL spikes appearance can not be directly related to regular injection of charge carriers from the electrodes and their transport across the device, as it is in the case of stationary EL. 

An important issue for the performance of an organic electronic device like an OFET is the injection of charge carriers, electrons or holes, from the electrode into the organic material. In case of the commonly used metal electrodes an efficient electron injection is possible only if the Fermi level of the metal and the energy of the lowest unoccupied molecular orbital (LUMO) of the organic material differs by a small amount only. A similar statement applies for hole injection, in this case the position of the highest occupied molecular orbital (HOMO) has to match with the position of the Fermi level. When noble metals, in particular Au, are being used for an electrode one may naively assume... 

The second study involved the local reduction or oxidation of an elec-trochromic material, tungsten oxide (33). This system is of particular interest since it has been the first system where the local injection of charge could be followed by an instantaneous change of color, making it possible to follow the process with an optical microscope. The stable form of tungsten oxide is W03, which is colorless and poorly conductive. The reduction of W03 [Eq. (5)] results in the formation of deep blue tungsten bronze that is substantially more conducting. 

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