Field heterojunction

Certain features in the PR spectra at 300 K from GaAs/Gai j,jAlj heterojunction bipolar transistor structures have been correlated with actual device performance thus PR can be used as an effective screening tool. From the observed FK oscillations it has been possible to evaluate the built-in dc electric fields in the Gai j jAlj emitter, as well as in the n—GaAs collector region. The behavior... 

Contacts are the elementary building blocks for all electronic devices. These include interfaces between semiconductors of different doping type (homojunctions) or of different composition (heterojunctions), and junctions between a metal and a semiconductor, which can be either rectifying (Schotlky junction) or ohmic. Because of their primary importance, the physics of semiconductor junctions is largely dealt with in numerous textbooks [11, 12]. We shall concentrate here on basic aspects of the metal-semiconductor (MS) and, above all, metal-insulator-semiconductor (MIS) junctions, which arc involved in the oiganic field-effect transistors. 

The use of interpenetrating donor-acceptor heterojunctions, such as PPVs/C60 composites, polymer/CdS composites, and interpenetrating polymer networks, substantially improves photoconductivity, and thus the quantum efficiency, of polymer-based photo-voltaics. In these devices, an exciton is photogenerated in the active material, diffuses toward the donor-acceptor interface, and dissociates via charge transfer across the interface. The internal electric field set up by the difference between the electrode energy levels, along with the donor-acceptor morphology, controls the quantum efficiency of the PV cell (Fig. 51). 

See also Field effect transistors (FETs) Heterojunction insulated gate FETs (HIGFETs), 22 164. See also Field effect transistors (FETs) Heterojunction photodiode arrays,... 

Field-effect transistors (FETs) Heterojunction bipolar transistors (HBTs) High electron mobility transistors (HEMTs) Metal oxide semiconductor FETs (MOSFETs) Single-electron transistors (SETs) Single-heterojunction HBTs (SH-HBTs) Thin-film transistors (TFTs) hydrogenated amorphous silicon in, 22 135... 

Heterojunctions of polythiophene with polypyrrole [195] and Cds [196] of the Schottky type were constructed and tested. The height of the barrier was 0.8 eV. The photogeneration of the charge carrier takes place in the depletion layer of the thiophene with consequent separation in the barrier electric field. 

The incorporation of siloles in polymers is of interest and importance in chemistry and functionalities. Some optoelectronic properties, impossible to obtain in silole small molecules, may be realized with silole-containing polymers (SCPs). The first synthesis of SCPs was reported in 1992.21 Since then, different types of SCPs, such as main chain type 7r-conjugated SCPs catenated through the aromatic carbon of a silole, main chain type cr-conjugated SCPs catenated through the silicon atom of a silole, SCPs with silole pendants, and hyperbranched or dendritic SCPs (Fig. 2), have been synthesized.10 In this chapter, the functionalities of SCPs, such as band gap, photoluminescence, electroluminescence, bulk-heterojunction solar cells, field effect transistors, aggregation-induced emission, chemosensors, conductivity, and optical limiting, are summarized. 

The piezoelectric field induces charge at the heterojunction. Even mi unintentionally doped (with low background doping density) AlGaN/GaN heterostructure has a piezoelectric-induced sheet charge in the GaN channel, which is found by electrostatic analysis to be... 

To obtain a better understanding of the effect of the mobility on the performance of a solar cell, a simplified model is introduced to provide an analytical description of the dependence of the short-circuit on the material parameters of the semiconductor for thin film bulk heterojunction solar cells. The following assumptions are suggested to give separate descriptions of the field current and diffusion current ... 

First, the drift current is calculated in the case of a constant electrical field, as one would expect for very thin bulk heterojunction solar cells. If the width W of the active layer is similar to the drift length of the carrier, the device will behave as a MIM junction, where the intrinsic semiconductor is fully depleted. The current is then determined by integrating the generation rate G = —dP/dx over the active layer, where P is the photon flux ... 

The generation of photoexcited species at a particular position in the film structure has been shown in (6.19) and (6.20) to be proportional to the product of the modulus squared of the electric field, the refractive index, and the absorption coefficient. The optical electric field is strongly influenced by the mirror electrode. In order to illustrate the difference between single (ITO/polymer/Al) and bilayer (ITO/polymer/Ceo/Al) devices, hypothetical distributions of the optical field inside the device are indicated by the gray dashed line in Fig. 6.1. Simulation of a bilayer diode (Fig. 6.1b) clearly demonstrates that geometries may now be chosen to optimize the device, by moving the dissociation region from the node at the metal contact to the heterojunction. Since the exciton dissociation in bilayer devices occurs near the interface of the photoactive materials with distinct electroaffinity values, the boundary condition imposed by the mirror electrode can be used to maximize the optical electric field E 2 at this interface [17]. 

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