Optimal dopant concentration

Quantitation of the impact of longer ion pair lifetimes on intermolecular charge separation can be made considering the collision frequency (Z) of the ion pairs and neutral dopants in the liquid crystal. The relations Dda = kBT/6nr a and Z = 4kBTNA/3r can be utilized to obtain the relation Z = 8DtwNa. Here, Dda is the diffusion constant of the neutral dopant, Na is the number density of the dopant, a is the radius of the dopant, and q is the viscosity [64], Dda can be estimated to be equal to the self-diffusion constant of the liquid crystal, which is 3 x 10-6 cm2/sec, a 10A, and the optimal dopant concentration for 3 is 4.3 x 1017 molecules/cm3. This gives a collision frequency of 3.2 x 106 sec-1, or... 

Fig. 3a shows etch depth per pulse versus absorption coefficient for PMMA/pyrene at various laser fiuences at 308 nm. As clearly seen, there exists an optimal dopant concentration for a given fluence. It should be noted that the high photoetching yield of PMMA/pyrene of 2.4 fi per pulse at F 1.2 J/cm obtained at 308 nm is not easily achievable at 193 nm on undoped PMMA, even at very high laser fiuences (19). The strong dependence of etch rates on absorption coefficients, with optimum values between 10 cm- and 10 cm-, is also found for PMGI/pyrene, and PMGI/ABH systems, as... 

Other features are consistent with non-phonon-mediated pairing in the hole-doped cuprates. The curve of vs. carrier concentration can be approximated by an inverted parabola with the maximum value of occurring at an optimal dopant concentration x (Uchida 1993). (Note that the terminology under-doped refers to values of x smaller than the optimally-doped value Xo, whereas over-doped refers values of x larger than Xo.) The isotope effect on Tc for optimally-doped material is essentially zero (i.e., Tc a with a wO M = ion mass) (Franck 1994). 

P. P. Dholabhai, S. Anwar, J. B. Adams, P. A. Crozier, and R. Sharma, Model. Simul. Mater. Sci., 20, 13 (2012). Predicting the Optimal Dopant Concentration in Gadolinium Doped Ceria A Kinetic Lattice Monte Carlo Approach. 

Here, we calculate the conversion efficiency of FGM having the optimized graded dopant concentration. Figure 3 shows the temperature dependent figure of merit (ZT) calculated for BiaTes with dopant concentration as a parameter. The ZT curve for the uniform material of dopant concentration is indicated by the solid line. It is... 

One limitation is that these detectors must, in general, be relatively thick. The dopant concentration must be low to preserve the semiconductor behavior - but with low concentrations the absorption is poor. If the detector thickness is less than 2 or 3 times the absorption length, the detectors will not absorb an appreciable fraction of the incoming photons - so the quantum efficiency (QE) will be low. Practical limits of the absorption constant for optimized IR detectors are l-10cm for Ge and 10-50 cm for Si. Thus, to maximize QE, the thickness of the detector crystal should be at least 0.5 cm for doped Ge and about 0.1 cm for doped Si. This makes the doped detectors impractical for use in an array. Si As is an exception - it can be used with detectors thin enough for arrays. 

Trilayer structures offer the additional possibility of selecting the emissive material, independent of its transport properties. In the case of small molecules, the emitter is typically added as a dopant in either the HTL or the ETL, near the interface between them, and preferably on the side where recombination occurs (see Fig. 13-1 c). The dopant is selected to have an cxciton energy less than that of its host, and a high luminescent yield. Its concentration is optimized to ensure exciton capture, while minimizing concentration quenching. As before, the details of recombination and emission depend on the energetics of all the materials. The dopant may act as an electron or hole trap, or both, in its host. Titus, for example, an electron trap in the ETL will capture and hold an election until a hole is injected nearby from the HTL. In this case, the dopant is the recombination mmo.-... 

For quantitative comparison of the grating strengths in the different liquid crystal composites, the first-order diffraction efficiency measurements of the Raman-Nath gratings are more amenable to analysis than the beam coupling ratio. Several concentrations for each of the dopants were utilized and Fig. 9 illustrates the highest diffraction efficiency values versus applied voltage for the samples with the optimal concentration of each dopant. A wavevector value of q = 1 x 103 cm-1 was again utilized. The first clearly noticeable fact is... 

Fig. 7.14. Resistivity vs. carrier concentration at 300 K of undoped and doped PLD ZnO thin films on sapphire [56]. The legend gives the maximum concentrations of the dopant oxides in the ZnO targets in weight-%. The optimized ZnO films show lower intrinsic n-type conductivity. For each dopant element, series of films grown at different PLD oxygen pressures are included...

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