Trap depth

The ultimate trapping site for a photoelectron is influenced by the high dielectric constant of silver haUde (ca 12.5, 11.15, and 7.15 for AgBr, AgCl, and P-AgI, respectively), the negative surface charge, and relative trap depths. Interior traps located at point defects on dislocation lines are probably not as... 

Figures 12-17 and 12-18 show the temperature dependencies of the mobility in a hopping system with a Gaussian DOS of variance <7=0.065 eV as a function of the relative concentration c of traps of average depth ,=0.25 eV and as a function of the trap depth E, at a fixed concentration < =0.03, respectively. For c=0...

Table 1. Trap depth and density in LPPP T , temperature at peak current, ,rsc and t J 1A are the trap levels obtained from the TSC and PIA experiments respectively, N, and it, are the number of traps and the trap concentration, respectively...

Figure 9-19. Bund diagram of LPPP with hole traps and gold electrodes with Va<- vacuum level. Ec conduction band, Eva valence band. E, Fermi level. . baudgup energy. and , " trap depths. ,( ) trap distribution, X electron affmity, and All work function of the gold electrodes.

Eq. (12.14) is recovered. The presence of traps lowers ihe mobility as expected. The essential message of Figures 12-17 and 12-18 is that, to a first order approximation, Eq. (12.14) maintains the icmperalurc dependency of the mobility if one replaces the disorder parameter by an effective disorder parameter ocJj or, equivalently, an effective width of the DOS that depends on both the concentration and the depth of the traps. Deviations from the behavior predicted by Eq. (12.14) become important for ,>0.3 eV, notably at lower temperatures. It is noteworthy, though, that the T- oo intercepts of p(7), if plotted as In p versus 7 2, vary by no more than a factor of 2 upon varying trap depth and concentration. 

The variation of o,.jj with trap depth is presented in Figure 12-19. The effect of traps on the mobility, reflected in an increase of acjj, becomes noticeable only above a certain critical trap depth that depends on concentration. Above that critical value, a2,.), increases approximately linearly with ,. Figure 12-20 shows complementary information concerning the effect of the trap concentration on a,. at constant trap depth. The data reproduces as a family of parallel straight lines on a (Pr/jlo)2 versus In c plot. Their intersection with the ov)jla— 1 tine indicates the critical concentration c, of traps of depth , needed to effect the mobility (see Fig. 12-21). 

Figure 12-20. The parameter (a,.jjla) vs. euncentration, parameiric in the trap depth K, (Ref. 1721).

A very important progress has been made recently on the theoretical background of the analysis of the transport problem also (2). Although it has been made clear that multi-trapping process is determining the carrier transport in the polymer, not only the nature of the trap but also the trap depth and the trap population are not definitely known even in pure poly-N-vinylcarbazole. The present report concerns with this problem. 

Fig. 4 (a) and (b) explain the principle. This is the thermally stimulated current to be used for the analysis of the trap depth and its population. In so far as the film has no experience of being heated above 110°C, the same film assembly could be used repeatedly many times with satisfactory reproducible results. 

In this way, the trap depth of the poly-N-vinylcarbazole was calculated as aE =0.56 eV and from the area of the 5°C peak the trap density was estimated to be of the order of 7 x 10l3 cm-3. 

On the methods of analysis of the thermally stimulated current and the values of the trap depth in poly-N-vinyl-carbazole... 

In summary, we have shown in [48] that we can account well for the trap depths of GG and GGG relative to that of G measured by Lewis et al. [56] with a model in which the wavefunction is not confined to the Gs but is still substantial on the surrounding bases. As in this case. The fit is insensitive to the value of the transfer integral, but requires that the difference between ionization potentials of adjacent G and A be -0.2 eV rather than -0.4 eV characteristic of the isolated bases. The small trapping found can be attributed entirely to the shallowness of the traps and, contrary to the assumption of [54], does not require different relaxation rates of the traps. 

Several methods not based on DLTS have also been described. White et al. (1976) present a two-light source, scanned photocapacitance technique that yields a spectrum of the deep states in the depletion region of a junction. The method is fast and sensitive, but most useful as a survey technique because knowledge of the dependence of the photoionization cross section on photon energy is required to obtain accurate trap depths. 

It is seen that Equation (5) is essentially that obtained by Weisz for the case of a large trap depth, with the addition of a term which gives the temperature dependence. 

If the electrons were simply trapped at the low temperature, the trap depth would have to be shallow enough to allow them to escape into the conduction band when the emulsion is warmed up hence, the trap depth would not exceed a few tenths of an electron volt. However, some electrons might combine with silver ions to form silver atoms even at the low temperature. When the emulsion is warmed up, these atoms either could dissociate... 

Mitchell (185) assigned to it the formula [irXg]- --2Ag, where Ag represents a silver ion vacancy. The complex acts as a transient electron trap. Eachus and Graves (191), from data obtained on Bridgman crystals, calculated a trap depth of 0.44 eV for the bromide complex in silver bromide. 

Further clustering of the solvent molecules near the deeper trap then occurs almost simultaneously causing a modest further increase of the trap depth. 

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