Type of Charge Carrier

Shallow donors (or acceptors) add new electrons to tire CB (or new holes to tire VB), resulting in a net increase in tire number of a particular type of charge carrier. The implantation of shallow donors or acceptors is perfonned for tliis purjDose. But tliis process can also occur unintentionally. For example, tire precipitation around 450°C of interstitial oxygen in Si generates a series of shallow double donors called tliennal donors. As-grown GaN crystal are always heavily n type, because of some intrinsic shallow-level defect. The presence and type of new charge carriers can be detected by Flail effect measurements. 

The conductivity becomes complex if mote than one type of charge carrier is present and involved in the conduction process. The total conductivity is the sum of all the conduction associated with the net motion of electrons, holes, and ions, ie ... 

Fig. 9.3 The charge distribution around pores in a low doped, illuminated n-type silicon electrode. Three types of charge carriers are present electrons, which are the majority carriers (dashes), holes, which are the minor-...

Conductivity requires a charge carrier. There are two types of charge carriers we will consider electrons and ions. The structural descriptions of Chapter 1 will be helpful in determining the primary type of charge carrier within a material, if any. In subsequent sections, we explore the molecular origins of each type of conductivity, investigate the important parameters that cause conductivity to vary in materials, and describe additional electrical conduction phenomena that have revolutionized our lives. 

One such device consists of two small islands of / -type semiconductor with and n-type silicon substrate. The islands are joined by a narrow / -type channel. The oxide portion of the MOSFET is an insulating layer of silicon dioxide that is formed by surface oxidation of the silicon. Gate, drain, and source connectors are attached. The MOSFET differs from the junction transistor in that a single type of charge carrier, either an electron or a hole, is utilized, instead of both. The conductivity of the channel... 

The activation energy of the conductivity can be obtained from a plot of Ln a against T-1 as shown in Fig. 2.20, where the presence of two zones presumably associated to the different types of charge carriers are observed. The values of the activation energy are 57 and 162 kJ mol-1 for P2tBCHM and 53 and 178 kJ mol-1 for P4tBCHM for low and high temperature zones, respectively. 

No reference has been made to the type of charge carrier and the equations developed so far in no way depend upon this. However, the electrical behaviour of solids depends very much on whether the charge carriers are electrons, ions or a combination of both. 

In the dark, the junction between an extrinsic (doped) semiconductor and a redox electrolyte behaves as a diode because only one type of charge carrier (electrons for n-type and holes for p-type) is available to take part in electron transfer reactions. The potential distribution across the semiconductor/electrolyte interface differs substantially from that across... 

Thus, it may be seen that, by reducing the particle radius, it is possible to obtain systems where transit from the particle interior to the surface occurs more rapidly than recombination, implying that quantum efficiencies for photoredox reaction of near unity are feasible. However, the achieving of such high quantum efficiencies depends very much upon the rapid removal of one or both types of charge carrier upon their arrival at the semiconductor surface, underlining the importance of the interfacial charge-transfer kinetics. This is the subject of the next section. 

In metals, where there is only one type of charge carrier, the Hall coefficient, Rb = (Ey / jxB), is very useful for measuring both the carrier density and the magnetic field B. Since the secondary field Ey and B are orthogonal, the Hall effect is a transverse effect and the Hall tensor is of rank three. It relates the axial vector Bj. to the antisymme-trical second-rank tensor Ey, which is equivalent to p yjx, where p y = PxyzBz-... 

Electrical conduction occurs by the long-range diffusion of either electrons or ions. Usually conduction by one or the other type of charge-carrier predominates, but in some inorganic materials both ionic and electronic conduction are significant. 

To describe the conductivity of an intrinsic semiconductor sample quantitatively, we need to calculate the concentrations of both types of charge carriers in the solid. The key quantity that controls the equilibrium concentration of electrons and holes in an intrinsic semiconductor is the band gap. Because the thermal excitation energy required to produce an electron and a hole is equal to Eg, the intrinsic carrier concentrations can be related to Eg using the Boltzmann relationship ... 

Before proceeding with this discussion, it is important to realize that there are two different types of charge carriers... 

Draw the band structure expected for germanium doped with gallium. What sort of semiconductor would this be What type of charge carrier has been added ... 

The high-temperature superconductors can be classified by the two different types of charge carrier positive and negative. In the former the charge carriers are positive holes, but in the latter they are electrons. Positive charge carriers are the most common. 

Once the charge carriers have been successfully separated, they need to be transported to the respective electrodes to provide an external direct ciu rent. Here the donor material serves to transport the holes whereas the electrons travel within the acceptor material. Thus, percolation paths for each type of charge carrier are required to ensure that the charge carriers will not experience the fate of recombination due to trapping in dead ends of isolated domains [60-62]. As such the bulk heterojunction has to consist of percolated, interpenetrating networks of the donor and acceptor phases. 

Bilayer devices [27,65] apply the donor-acceptor concept introduced above here the exciton is dissociated at their interface, leading to holes on the donor and electrons on the acceptor. Thus, the different types of charge carriers may travel independently within separate materials and bimolecu-lar recombination is largely suppressed. Therefore fight intensity-dependent... 

These solid solutions have several types of charge carriers. They can be represented by anions, cations, electrons, and holes. The Ohm law is fair for each of them. The full current represents itself as a summary of the partial currents by n particles ... 

Finally, a low work function metal is vacuum deposited as the cathode for electron injection. Upon application of a voltage, both types of charge carriers (electrons and holes) are injected and move towards each other by hopping [1], Once a hole and an electron meet on an active site they combine to form an exciton, which can relax to... 

In deriving this equation, it was assumed that only one type of charge carrier was present. However, in principle, any mobile charged species can... 

All the types of charge carriers present in a medium contribute to the conductivity. In the case of semiconductors, both electrons and holes should be taken into account when conductivity is calculated, and the expression for the conductivity becomes (using Eqs. 7.6 and 7.7). 

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