Injection of carriers

Fig. 2. Schematic diagram of active layer stmctures employed in LEDs under forward bias showing the conduction band (CB) and valence band (VB). The simplest devices employ (a) a homostmcture active layer wherein the bandgap is constant throughout the device. More advanced stmctures consist of (b) single and (c) double heterostmctures. Heterostmctures faciUtate the confinement and injection of carriers in the active region where the carriers may...

Table 18—Concentration of uCe in the tissues of adult mammals after injection of carrier-free MCeCl3 (pH = 3) b... 

Table 19—Deposition and concentration of, 44Ce in the tissues of adult mice and ratsk after injection of carrier-free, 44CeCl3...

If the dephasing time of the coherent phonons depend critically on the carrier density, photo-injection of carriers with the second pump pulse can annihilate them partially or completely, depending on its fluence but not on its relative timing. Such incoherent control was demonstrated for the LO phonons of GaAs [37],... 

Here Jo is the dark saturation current density, Rs is the series resistance, A is the area and Rp is the shunt resistance. When a voltage V exists on the junction, the output current of the illuminated solar cell has two components, (1) the junction current density 7j (illumination) due to injection of carriers and (2) the short circuit current density Jsc due to light generated carriers. Therefore the output current density J v of the illuminated solar cell is given by,... 

Ultrafast injection of carriers into the UO2 substrate suggests that overall cell efficiency is not limited by this process but by intervening transfer mechanisms (e.g., trapped state populations reducing quantum yield) or longer time scale electron-dye recombination rates (typically taking microseconds). For example, it was found that the absorbed photon to current efficiency (APCE) is considerably reduced for V compared to IV under identical cell conditions (27,55). While V has a 350 mV lower electrochemical reduction potential than IV (and hence a red-shifted absorption spectrum), it is unclear why the redder absorbing dye (V) does not inject as efficiently (56). Recent visible excitation with broadband... 

Whereas early publications have explained experimental results within the framework of the Fowler-Nordheim mechanism alone [43], recent publications [44-46] have attributed the injection of carriers to a combination of both mechanisms at low fields and high temperature, thermoionic emission is considered dominant. On the contrary, for high electric fields (typically >2MV/cm), injection would essentially occur via tunneling. 

For bulk semiconductors and multiple quantum well structures (one-dimensional confined semiconductors), transport properties are of great interest and are important for practical applications such as transistors and detectors. Semiconductor nanoclusters are usually confined in three-dimensions by insulating matrices such as polymers and glasses, where the transport of carriers is not feasible. To explore transport-related applications of semiconductor clusters, a matrix that is capable of transporting carriers is needed, In addition, the redox properties of the matrix have to allow injection of carriers from semiconductor nanoclusters to the matrix. 

Usually the absence of surface charging associated with the dark injection of carriers from the electrodes into the bulk of the dm (holes in case of positively charged free surface), leading to a sharp increase in dark conductivity. The increase in the value of V at the positive charge indicates blocking of the dark hole injection from the free surface when N > 34. The most probable reason is the appearance in the dm bulk near the electrode positively charged layer of stabilized cation-radicals (electrode polarization). The latter are holes (h+) trapped by deep centers ... 

Guinea pigs received an intraventricular injection of carrier-free nd were killed two hours later. At this time... 

In conducting polymers, the extra carriers added upon doping are able to drift under an applied electrical field. In semiconducting polymers, no carriers are available except those thermally excited across the gap. However, negative (positive) carriers can be injected into the material by metallic contacts when the barrier between the metal work function and the LUMO (HOMO) molecular levels is overcome. Then, the injected carriers can move inside the semiconductor if a bias field is applied. Injection of carriers and their transport is a fundamental issue for all electronic devices and transistors in particular. In the following, main transport properties of organic semiconductors (both small molecules and polymers-based) used as active materials in transistors will be reviewed. 

Many techniques have been applied in attempts to optimise the performance of organic LEDs. Electron and hole transporting films have been deposited between the cathode and the emitting layer and the anode and the emitting layer, respectively, to improve and balance the injection of carriers [5]. The use of low work function cathode materials such as calcium [6] or Mg/Ag [7] has led to high efficiency devices. These metals are unstable on exposure to air, however. 

Pressure change in the headspace bottle varies with the action of the syringe plunger (volume removed) on sample removal from the sealed bottle, compensation by injection of carrier gas necessary. 

An injection of carriers only occurs if an extrinsic photogenerator is used together with a charge transporting material. Usually dye particles are dispersed in a... 

Doping (through oxidation or reduction) leads to injection of carriers... 

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