Charge carrier transport interfaces

In this section, we have assumed that the limiting transport current of electrons or holes in semiconductor electrodes is much greater than the ion transfer current across the electrode interface. When the minority charge carrier transports charge... 

Thus, in a region in which the current density at a driven semiconductor/solution interface is low enough that the electrons in the semiconductor are in equilibrium between surface and bulk (i.e., not rate-determined by charge carrier transport—... 

Solar cells, or photovoltaic devices, have been studied for many years [3], Most of the current work is focused on dye-sensitized nanocrystalline solar cells. These provide a technical and economically viable alternative to present-day photovoltaic devices. In contrast to conventional systems, in which the semiconductor assumes both the task of light absorption and charge carrier transport, the two functions are separated in dye-sensitized nanocrystalline solar cells [54] (cf. OPCs). Light is absorbed by the dye sensitizer, which is anchored to the surface of a wide-band-gap semiconductor. Charge separation takes place at the interface via photoinduced electron injection from the dye into the conduction band of the... 

The charge carrier transport model of the CoFe/MgO/CoFe nanostructure taking into account the Schottky barrier and interface charge was developed. TMR and 1-V characteristics were calculated on the basis of experimental data and modeled for different parameters of the nanostructure. Estimates of TMR are realized through the variation of height of the effective barrier for spin-up and spin-down electrons. Growth of TMR is 0.18, 0.40 and 0.55 when the energy difference between barriers is 0.02 eV, 0.05 eV and 0.10 eV, respectively. 

I-V characteristics and TMR for CoFe/MgO/Si nanostructure were modeled based on the charge carrier transport taking into account Schottky barrier and interface charge states. TMR can reach 5-25% in the range of external biases of... 

In addition to the morphological features of the pentacene layer, the performance of an OTFT is influenced by the microscopic interface environment at the interface between the pentacene layer and a source and drain metallic contact. The electronic parameters of the interface may give rise to an increased contact resistance. Therefore it is important to understand the relationship between the chcrnical/structural characteristics of the OS/metal interface and charge carrier transport in OTFT. For example the difference in mobility between the top-contact and bottom-contact OTFT was associated to the different morphology of the pentacene layer near the metallic contacts [13],... 

V. I. Arkhipov, E. V. Emelianova, and H. Bassler. Charge carrier transport and recombination at the interface between disordered organic dielectrics. /. Appl. 

Charge carrier transport in the electrode-oxide semiconductor interfaces... 

Excitation can also occur in molecules directly adsorbed and acting as a mediator at the semiconductor interface. In this dye sensitization mode, the function of light absorption is separated from charge carrier transport. Photoexcitation occurs at the dye and photogenerated... 

This proposal was in line with the improved luminance efficiency identified as the result of an enhanced balance in the charge carrier transport properties. In this case, it was proposed that the electrons would spread into the semiconductor, thereby causing the halide to be detached from the polymer backbone on contact formation between the cathode material and the PPV. The anions produced in this way would drift either in the self-induced electric field established by the cathode close to the electron reservoir, or in the external electric field. The subsequent precipitation that would be expected to occur would result in a chemical modification of the interface region of the contact materials that, ultimately, would cause aging and fatigue of the device. 

The charge carrier balance problem has been minimized by the introduction of multilayered polymeric structures that produce potential barriers at the internal interfaces. These potential barriers impose restrictions to charge carrier transport through the device and enhance the recombination probability and, consequently, the device efficiency. One example of such a structure is the rrO/PPV/CN-PPV/metal LED. CN-PPV presents a higher electroafiinity and ionization potential than PPV, so that there is a potential barrier for electron transport from the CN-PPV to the PPV and a potential barrier for holes in the opposite direction [218]. Several other conjugated polymers and molecules are also used in combination with PPV in heterolayer LEDs [213]. 

Only recently it has been discovered that electronic states at the dielectric interface substantially determine the charge carrier transport in organic field-effect transistors. Pentacene is a prominent example where the unique p-type behavior of pentacene based OFETs has been attributed to the organic semiconductor alone and where the influence of electronic interface states at the pentacene/insulator surface has been overseen. The reason for this was the belief that organic semiconductors are unable to form dangling bonds at the interface, which are the main cause for interface states in inorganic semiconductors. However, there are other forms of interface states which can act as efficient charge carrier traps. 

The unveiled strong impact of dielectric interface states on the OFET charge carrier transport properties leads to the question if directed dielectric interface engineering can be utilized to modify the ambipolar charge carrier transport for organic CMOS applications. 

Benson N, Schidleja M, Siol C, Melzer C, von Seggem H (2007) Dielectric interface modification by UV irradiation a novel method to control OFET charge carrier transport properties. Proc SPIE 6658 0Wl-9... 

The first step, particle formation by gas or liquid phase synthesis, leads to particles which are further functionalized at their surface to ensure colloidal stabilization and to allow charge transfer across particle—particle interfaces in the final layer. The surface and electronic properties of the particles are typically characterized by a whole set of techniques including time-resolved measurements of charge carrier transport. The best way of cost-efficient... 

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