Mobility, charge carrier measurement

Direct contact techniques do not work with electrolytic solutions. One cannot, for example, measure the resistance of salt water in a cell with an ordinary ohmmeter. This is due to the fact that the mobile charge carriers in an electrolytic solution are ions, not electrons. The conversion of ionic to electronic conduction at the electrode interface can only take place through an electrochemi-... 

The surface field effect can be realized in a number of ways. The semiconductor can be built into a capacitor and an external potential applied (IGFET), or the field can arise from the chemical effects on the gate materials (CHEMFET). In both cases, change in the surface electric field intensity changes the density of mobile charge carriers in the surface inversion layer. The physical effect that is measured is the change in the electric current carried by the surface inversion layer, called the drain current. 

An example is the photoannealing of Ge 22 Irradiation with electrons of 4 MeV at 77 °K converts n-conducting samples of Ge to p-type Ge. The p-con-ducting Ge is annealed at temperatures between 77 and 300 °K in the dark or in white light. Hall effect and conductivity measurements are used to determine sign and concentration of the mobile charge carriers. In the temperature range between 77 and 93 °K, illumination produces a decrease in conductivity. How-... 

Microwave absorption and luminescence decay measurements have been independently carried out to monitor the charge injection from excited Ru(bpy)2-(dcbpy)2+ into Sn02, ZnO, and Ti02 nanocrystallites [245]. Since microwave conductivity arises as a result of mobile charge carriers within semiconductor particles it is possible to probe the charge injection process by monitoring the growth in the microwave absorption [178]. 

This equation states that the electrical conductivity due to a free carrier is the product of the charge on the carrier, q, its concentration in the solid, and its mobility, fx. Since semiconductors have two different types of mobile charge carriers, electrons, and holes, the total sample conductivity, a, is simply the sum of the individual conductivities due to each carrier type. It should be noted that the conductivity depends only on the absolute number of carriers, and therefore is not affected by the signs of the carriers themselves. Carrier mobilities for electrons and holes in a variety of semiconductors can be measured experimentally. These values have been tabulated in various reference books and are available for many semiconductors of interest. Doping of a semiconductor therefore allows precise control over the conductivity of the semiconductor sample. 

Reported studies deal with measurements of the electrode potential of zero charge Epzc [698, 699], double layer investigations [700-702] and studies of electrode reaction mechanisms [703, 704] for an overview, see also [693, 697], Numerous studies (beyond many conducted ex situ) deal with intrinsically conducting polymers, particularly photogenerated mobile charge carriers [705-707]. 

In general, only one mobile charge carrier, either electrons or holes, is present. In this case, by measuring both the conductivity, a, and the Hall coefficient, Ru, it is possible to determine the number of charge carriers and their mobility as ... 

The measured properties of polycrystalline ceramics are greatly influenced by the microstructure of the material. Of particular importance are the grain size of the crystallites, porosity, voids or gas bubbles within the ceramic and any impurity phases present. In addition, chemical defects such as point defects and mobile charge carriers within grains and the physics and chemistry of the grain botmdaries will all have an influence on the measured properties of the solid. Because of this, ceramics are subjected to carefully controlled fabrication routes and the sintering temperature and time have a considerable effect upon the measured properties (Figure 6.3c). 

The dependence of the dc conductivities and the parameters derived thereof show that there are distinct differences between the ion dynamics in PDADMAC-rich and PSS-rich PEC. In both cases, however, the Arrhenius dependence of clearly shows that the ion dynamics in PEC materials is determined by the thermally activated hopping processes of the mobile ions. The fact that the isothermal dc conductivity increases continuously with NaPSS content indicates that the chloride ions do not dominate the ion transport, even in PEC materials with an excess of polycations and thus Cl as the most abundant mobile charge carrier. Otherwise, aac as a function of x should pass through a minimum, which is obviously not seen experimentally. The conductivity measured for PEC with x < 0.50 could therefore be either due to residual Na ions or protons. To shed more light on this aspect, PEC in which the sodium ions were replaced by lithium or cesium ions were studied. These results are discussed in the following section. 

With a combination of in situ conductivity and potential-step chronocoulometric measurements, Harima et al. [988] studied the enhancement of carrier mobilities in poly(3-methylthiophene). In addition to the obvious effect of the electrochemically induced increase in the concentration of mobile charge carriers, a drastic mobility enhancement of over 4 orders of magnitude, which implies a change from hopping to metallic transport, was concluded. 

Determination of G by measurement of the radiation-induced low field conductivity requires, besides information on the absorbed dose rate, the knowledge of the recombination constant and of the mobilities of the charge carriers. Measurement methods for these transport properties are described in Chapter 3. 

Measurements of thermally stimulated cirrrents in our ladder-type polyphenylenes probe the density of mobile charge carriers after detrapping and reveal extremely low trap densities [136,137]. 

In order to compensate the initially proposed interfacial electron traps on the Si02 dielectric, Ahles et al. [62] introduced traces of Ca to the Si02 dielectric interface. As a low work function metal, Ca was believed to act as an electron donor saturating traps in the interface near pentacene layer. The capability to accumulate mobile charge carriers at the newly engineered interface can again be examined by MIS diode experiments. The result of impedance measurements on a MIS diode... 

---