Carrier mobility determination

The photocurrent stimulated is limited in all of these processes by die rate of carrier production (light intenaty dependent) or by the carrier mobilities, or both. Systems in which the current is limited entirely by the rate of carrier gmeratim are termed emission limited, whilst if carrier mobility determines the current it is space-charge limited (SCLC). Indicative of the onset of SCLC is supralinearity in the current-voltage dependence theoretically I then varies as V. ... 

The electrical conductivity in the solid state is determined by the product of the carrier concentration and the carrier mobility. In conjugated polymers both entities are material dependent and, i.e., are different for electrons and holes. Electrons or holes placed on a conjugated polymer lead to a relaxation of the surrounding lattice, forming so-called polarons which can be positive or negative. Therefore, the conductivity, o, is the sum of both the conductivity of positive (P+) and negative polarons (P ) ... 

Silicon conversion table. For conversion of substrate doping density to resistivity, and vice versa, and to determine carrier mobility, position a ruler vertically over the chart. For a certain doping density (ordinate) and applied bias (solid lines) the depletion region width (left abscissa) and capacitance (right abscissa) are given. The distance between two dopant atoms is shown (broken line, left abscissa) idealizing the positions of the dopants to be in an fee lattice. 

Typical photocurrent transients are shown in Fig. 6 for electrons and in Fig. 7 for holes. The shape of these curves is representative for all transients observed in the study and is characteristic of dispersive transport [64-68]. The carrier mobility p was determined from the inflection point in the double logarithmic plots (cf. Fig. 6b and Fig. 7b) [74]. TOF measurements were performed as a function of carrier type, applied field, and film thickness (Fig. 8). As can be seen from Fig. 8, the drift mobility is independent of L, demonstrating that the photocurrents are not range-limited but indeed reflect the drift of the carrier sheet across the entire sample. Both the independence of the mobility from L, and the fact that the slopes of the tangents used to determine the mobility (Fig. 6 and Fig. 7) do not add to -2 as predicted by the Scher-Montroll theory, indicate that the Scher-Montroll picture of dispersive transients does not adequately describe the transport in amorphous EHO-OPPE [69]. The dispersive nature of the transient is due to the high degree of disorder in the sample and its impact on car-... 

As expected, the coordination of Pt markedly influences the photophysical characteristics of the PPE. The photoluminescence is efficiently quenched, and the absorption maximum in the visible regime experiences a hypsochromic shift. The charge-carrier mobility of different EHO-OPPE-Pt samples was determined by TOE measurements as described above for the neat EHO-OPPE. The shape of the photocurrent transients of all EHO-OPPE-Pt samples was similar to those shown in Figs. 6 and 7 for the neat EHO-OPPE. This indicates that these organometallic conjugated polymers networks are also characterized... 

Charge mobilities determined by the time of flight (TOF) method show that values of 1-10 cm s are not rare for MOMs (Karl et al, 1999). In TOF experiments the transit time r for a sheet of photoinjected carriers to move across a sample of thickness L is monitored. The sheet of carriers is usually generated... 

The study of the dispersion of photoinjected charge-carrier packets in conventional TOP measurements can provide important information about the electronic and ionic charge transport mechanism in disordered semiconductors [5]. In several materials—among which polysilicon, a-Si H, and amorphous Se films are typical examples—it has been observed that following photoexcitation, the TOP photocurrent reaches the plateau region, within which the photocurrent is constant, and then exhibits considerable spread around the transit time. Because the photocurrent remains constant at times shorter than the transit time and, further, because the drift mobility determined from tt does not depend on the applied electric field, the sample thickness carrier thermalization effects cannot be responsible for the transit time dispersion observed in these experiments. 

The charge transport in amorphous selenium (a-Se) and Se-based alloys has been the subject of much interest and research inasmuch as it produces charge-carrier drift mobility and the trapping time (or lifetime) usually termed as the range of the carriers, which determine the xerographic performance of a photoreceptor. The nature of charge transport in a-Se alloys has been extensively studied by the TOF transient photoconductivity technique (see, for example. Refs. [1-5] and references cited). This technique currently attracts considerable scientific interest when researchers try to perform such experiments on high-resistivity solids, particularly on commercially important amorphous semiconductors such as a-Si and on a variety of other materials... 

It is useful to have a means of determining overall electrical quality, i.e., the ability of the sample to conduct current in the intended manner. In general, electrical performance is limited by two problems (1) unwanted impurities or defects, and (2) inhomogeniety. Both of these problems can affect the carrier mobility, which thus becomes an important parameter to measure. In bulk, SI GaAs it is not too uncommon to measure room temperature electron mobilities of 1500 cm2/V s or less (cf., for example, sample MA 287/80 of Table II). One must first be sure that this low a value is not simply due to mixed conductivity, a phenomenon discussed in Sections 2 and 18. If p 4 x 10 fl cm, then mixed conductivity is probably not important (Look,... 

There is one other means of determining lifetime, available if both photo-Hall (PH) and absorption experiments can be carried out. This possibility is simply illustrated by Eq. (35). Here the PH measurement gives An, the absorption measurement gives ocB, and f0 can be easily measured with a calibrated light detector. An obvious caveat here, of course, is that we must assume that a = aB, i.e., that all of the light absorption is due to electronic transitions. For above-band-gap light this assumption will almost certainly be true. It was seen before that absorption measurements can be useful in determining impurity concentrations. Thus, a combination of PH and absorption data may yield both N and rB. If the carrier mobility can... 

The specific application of a material generally determines the particular structure desired. For example, hydrogenated amorphous silicon is used for solar cells and some specialized electronic devices (10). Because of their higher carrier mobility (see Carrier Transport, Generation, and Recombination), single-crystalline elemental or compound semiconductors are used in the majority of electronic devices. Polycrystalline metal films and highly doped polycrystalline films of silicon are used for conductors and resistors in device applications. 

Experimentally, the charged carrier mobility can be determined by a time of flight (TOF) technique (for details see [28]). 

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