Hole drift mobility temperature dependence

Fig. 3.13. Temperature dependence of the (a) electron and (b) hole drift mobility at different applied fields ranging from 5 x 10 V cm" to 5 X 10 V cm". The field dependence of is caused by the dispersion (Marshall et al. 1986, Nebel et al. 1989).

Strong Field Dependence of Drift Mobility. Hole drift mobility increases sharply with field, and with PVK, a characteristic E dependence of log (X is exhibited, as originally reported by Pai (36), whose data are displayed in Figure 5. Drift mobility values are low and fall into the range cm /V-s at room temperature. 

Strong Temperature Dependence of Drift Mobility. Figure 6 is an Arrhenius representation of hole drift mobility data on a 0.2 1 TNF-PVK film (iO). The apparent activation in this representation is field dependent,... 

Numerous studies of charge transport in amorphous molecular materials have shown that hole drift mobilities of amorphous molecular materials vary widely from 10 6 to 10 2 cm2 NT1 s 1 at an electric field of 1.0 X 105 V cm-1 at room temperature, greatly depending upon their molecular structures. Table 7.6 lists hole drift mobilities of some amorphous molecular materials that function as holetransporting materials in OLEDs. 

Fig. 12. Temperature dependence of the hole drift mobility. Solid Unes are theoretical fits as discussed in the text. A, 17 V , 4 V O, 1 V. [Reprinted with permission from Solid State Communications, Vol. 47, T. Tiedje, B. Abeles, and J. M. Cebulka, Urbach edge and the density of states of hydrogenated amorphous silicon, Copyright 1983, Pergamon Press, Ltd.]...

Fig. 3. Field dependence of the hole-drift mobilities in PDS(Th)4 at room temperature.

Fig. 5.29. Temperature dependence of the electron and hole drift mobilities in vitreous Se at two pressures (after Dolezalek and Spear, 1970).

By using higher injection levels and the theories (Many and Rakavy (1962) Helfrich and Mark (1962)) which take account of the resulting space charges, Rossiter and Warfield (1971) were able to extend the drift velocity measurements to 78 K. As shown in Table 5.4 the observed activation energy for holes is 0.095 eV, considerably smaller than those of other workers. They find, moreover, a break in the T-dependence of for holes at 150 K. Below this temperature the activation energy is only 0.0093 eV. In addition, they report a small field dependence of the hole drift mobility for fields in excess of 10 V/cm. This had not been seen by the earlier groups. 

It was established that the elevated hole drift mobility of DCZB polymers is due to the reduced concentration of trapping sites which are in fact excimer-forming sites. This was confirmed by the temperature and electric field dependencies of the hole mobility. These observations support the idea that eharge transport and exciton transport have... 

Figure 20 (a-c) Drift and diffusion of optically excited carriers in P-rhombohedral boron. Densities of electrons, electron-bole pairs, and boles at different distances from tbe illuminated surface versus transit time related to the onset of steady-state optical excitation (112). (d) Temperature dependence of the hole drift mobility in P-rhombohedral boron derived from transient photoconduction (113). 

The temperature dependence of the hole drift mobility (Fig. 20d) yields a thermal activation energy of 240 meV Q13). 

The drift mobility in this dispersive regime has an unusual electric field and thickness dependence. Fig. 3.13 shows the field dependence of the electron and hole mobility at different temperatures (Marshall et al. 1986, Nebel, Bauer, Gom and Lechner 1989). The electron drift... 

Fig. 7.9. Temperature dependence of the acousto-electric voltage, and drift mobility of (a) electrons and (b) holes obtained by the SAW technique, llie solid lines are calculated for trapping in an exponential band tail of slope 7J. or 7 (Takada and Fritzsche 1987).

With increasing drift velocity, the mobilities at low temperature become however dependent on the electric field strength in a characteristic manner they decrease with increasing field. According to Eq. (8.4), the drift velocity vd then increases sublinearly with increasing field strength. Figure 8.37 shows a typical example for the drift velocity v of the holes in an ultrapure naphthalene crystal as a function of the electric field at different low temperatures [20]. 

Fig. 8.37 The dependence of the drift velocity Vq of the holes on the electric field F in a naphthalene crystal at low temperature in the range of non-Ohmic transport. The slopes at the origin correspond to the zero-field mobilities /x(F 0) = 420 cm /Vs at 19 K,...

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