Effective trap density

Determination of material parameters gain factor T, effective electro-optic coefficient (( reff) and effective trap density AAir... 

The scattering pattern contains additional information about the scattering process itself as well as for the determination of material parameters. We will demonstrate in the following, that both the angular dependence of the holographic gain and the product of the effective linear electro-optic coefficient with the electron-hole competition factor as well as the effective trap density can be determined from the spatial distribution of the scattering pattern as a function of temperature [7],... 

In general, the diffusion equation depends on all the microscopic parameters. The microscopic parameters of van Kampen s model are the local values of the effective trap density cr, which is density times cross-section and work function . The traditional diffusion relation of Eq. (6.305) is valid only for isotropic diffusion and under the restrictive conditions that cr cx exp( homogeneous system with nontrivial geometry. Equation (6.306) is valid when the effective trap concentration is constant, which is more realistic for liquids. 

Apart from fundamental constants and the liquid temperature, the variable parameters in the effective mobility equation are the quasi-free mobility, the trap density, and the binding energy in the trap. Figure 10.2, shows the variation of prff with e0 at T = 300 K for /tqf = 100 cm3v 1s 1 and nt = 1019cm-3. It is clear that the importance of the ballistic mobility (jl)l increases with the binding... 

In comparing the results of the quasi-ballistic model with experiment, generally pq[ = 100 cn v s-1 has been used (Mozumder, 1995a) except in a case such as isooctane (Itoh et al, 1989) where a lower Hall mobility has been determined when that value is used for the quasi-free mobility. There is no obvious reason that the quasi-free mobility should be the same in all liquids, and in fact values in the range 30-400 cmV -1 have been indicated (Berlin et al, 1978). However, in the indicated range, the computed mobility depends sensitively on the trap density and the binding energy, and not so much on the quasi-free mobility if the effective mobility is less than 10 crr v s-1. A partial theoretical justification of 100 cm2 v 1s 1 for the quasi-free mobility has been advanced by Davis and Brown (1975). Experimentally, it is the measured mobility in TMS, which is considered to be trap-free (vide supra). 

Table 10.4 lists the values of trap density and binding energy obtained in the quasi-ballistic model for different hydrocarbon liquids by matching the calculated mobility with experimental determination at one temperature. The experimental data have been taken from Allen (1976) and Tabata et ah, (1991). In all cases, the computed activation energy slightly exceeds the experimental value, and typically for n-hexane, 0/Eac = 0.89. Some other details of calculation will be found in Mozumder (1995a). It is noteworthy that in low-mobility liquids ballistic motion predominates. Its effect on the mobility in n-hexane is 1.74 times greater than that of diffusive trap-controlled motion. As yet, there has been no calculation of the field dependence of electron mobility in the quasi-ballistic model. 

But one can ask the question why normal muonium is observed at all if the global energy minimum (i.e., the stable site) is really at the bond center (anomalous muonium). On the time scale of the muon lifetime, relaxations of the Si atoms may be sufficiently slow to effectively trap the muon in the low-density regions of the crystal, where relaxation of the host atoms is... 

Chung, G. Y., et al., Effect of Nitric Oxide Annealing on the Interface Trap Densities Near the Band Edges in the 4H Polytype of Silicon Carbide, Applied Physics Letters, Vol. 76, No. 13, March 27, 2000, p. 1713. 

The activation energy observed experimentally is the effective activation energy and is a function of applied voltage V and trap density Hb. Several interesting features predicted by this equation are given below. 

Here is the hole trap density, g is the degeneracy factor (taken as unity in the calculations), Etp is the ionization energy of the hole traps, Ev is the valence band edge (i.e. HOMO), Ny is the effective density of states for holes, at is the standard deviation of the Gaussian distribution of traps, and the factor expOS /F/fcr) arises due to the Poole-Frenkel effect. Analytical solution of (3.58) and (3.60) can not be obtained. Numerically computed results are shown in Fig. 3.29. 

Generally, traps are expected to yield field-effect mobilities which are both much lower than microscopic ones and varying with physical or electrical parameters. It would be worth taking this into account in CP TFT data. Apparently, low threshold voltages will require trap densities in the range 1017 cm-3, or less than 100 ppm, for trap depths of a few tenths of 1 eV. This does not seem impossible but the very low localized level densities sometimes quoted seem unrealistic, considering the poor structural order and limited chemical purity of most CPs to date. 

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