Holes mobility

Hog fat Hohlraum H-Oil process Holding furnaces Hole mobilities Hollander beater Hollandite [12008-99-0]... 

Liquid Crystalline Systems. Conventional photoconductive polymers are amphorous or systems withlow order. In the case of PVK, the hole moves by hoppiag between the pendent carba2ole groups. The hole mobilities are usuaUylow, cm /Vs, due to a trap-dominated hoppiag... 

With the Monte Carlo method, the sample is taken to be a cubic lattice consisting of 70 x 70 x 70 sites with intersite distance of 0.6 nm. By applying a periodic boundary condition, an effective sample size up to 8000 sites (equivalent to 4.8-p.m long) can be generated in the field direction (37,39). Carrier transport is simulated by a random walk in the test system under the action of a bias field. The simulation results successfully explain many of the experimental findings, notably the field and temperature dependence of hole mobilities (37,39). 

Based on the Monte Carlo simulations, it is seen that the presence of positional disorder causes the mobiUty to decrease with increasing field at low fields (37). This is the case because the introduction of positional disorder into the system provides the carrier with energetically more favorable routes, which occasionally are against the field direction. These detour routes are most efficient at low fields, but are eliminated at high fields. This rationalizes the decrease of hole mobilities with increasing field. 

Experimental Hole Mobilities. The experimental values of hole mobihties in polymers are tabulated in Tables 1 and 2. The hole mobihty is field dependent. Whenever the experimental data have been fitted with equation 5, the parameters p.Q, O, and O, which give a complete description of the field dependence of the hole mobihty, are Hsted (Table 2). Otherwise, hole mobilities at selected fields are Hsted. All acronyms are defined in Figures 2 and 3. 

Table 1. Hole Mobilities of Selected Molecular and Polymeric Materials ...

Table 2. p-QjCt, and E and Some Hole Mobilities, cm /V s, of Selected Molecular and Polymeric Materials ... 

Cryoelectronics. Operation of CMOS devices at lower temperatures offers several advantages and some disadvantages (53). Operation at Hquid nitrogen temperatures (77 K) has been shown to double the performance of CMOS logic circuits (54). In part, this is the result of the increase in electron and hole mobilities with lower temperatures. The mobiHty decreases at high fields as carrier speeds approach saturation. Velocity saturation is more important for cryoelectronics because saturation velocities increase by only 25% at 77 K but saturation occurs at much lower fields. Although speedup can... 

Once values for R , Rp, and AEg are calculated at a given strain, the np product is extracted and individual values for n and p are determined from Eq. (4.19). The conductivity can then be calculated from eq. (4.18) after the mobilities are calculated. The hole mobility is the principal uncertainty since it has only been measured at small strains. In order to fit data obtained from elastic shock-loading experiments, a hole-mobility cutoff ratio is used as a parameter along with an unknown shear deformation potential. A best fit is then determined from the data for the cutoff ratio and the deformation potential. 

Figure 9-26. Expcrimenial and calculated (solid lines) UV characteristics of ITO/PPV/Au hole-only devices of various thicknesses, L. The current flow in all devices is described by SLC with a hole mobility //, = 1(r cm2 V"1 s 1 and with a dielectric constant of 3. The inset shows the chemical structure of the PPV investigated in that study (R =CHi, R2=CiUH2i). Reproduced from Ref. 185).

Two main methods have been used to measure the charge carrier mobility in electroluminescent polymers time of flight (TOF) carrier transit time measurements and analysis of the current-voltage (1-V) characteristics of single carrier devices in the space charge-limited current (SCLC) regime. A summary of the results for the hole mobility of PPV and PPV-related polymers is given in Table 11-1 [24, 27-32]. For... 

Figure 12-10. j(V) characteristics of ITOIPPVIAu hole only devices with thicknesses T=0.13 pm (squarcs)=3 pm (triangles), and 0.70 pm (dots). Full lines represent the prediction of Child s law (Eq. (12.5) for a hole mobility of 5xl0 7cnr V"1 s and a dielectric constant c=3. The inset shows the PPV used with R,=CH3 and ft2=Cu)ll21 (Ref. [411). 

Figure 12-27. Temperature dependence of the hole mobility in DPOP-PPV at different electric fields Dale for T= 0 have been obtained by extrapolation. The inset shows the intersection of Arrhenius plots at T()=465 K (Ref. 1831).

Studies of double carrier injection and transport in insulators and semiconductors (the so called bipolar current problem) date all the way back to the 1950s. A solution that relates to the operation of OLEDs was provided recently by Scott et al. [142], who extended the work of Parmenter and Ruppel [143] to include Lange-vin recombination. In order to obtain an analytic solution, diffusion was ignored and the electron and hole mobilities were taken to be electric field-independent. The current-voltage relation was derived and expressed in terms of two independent boundary conditions, the relative electron contributions to the current at the anode, jJfVj, and at the cathode, JKplJ. 

Figure 13-14. Spatial profiles of the carrier densities and the recombination for devices of width 100 nrn (dotted lilies) and 10 pm (solid lilies), for equal electron and hole mobilities. Reproduced with permission from I05J. Copyright I99K by the American Physical Society.

The dominant parameters for charge earner injection are the height of the potential barrier at the interface polymer/hole injection contact and the hole mobility of the polymer. 

According to that model, the net current flow in the device therefore can be increased in bilayer structures using a hole-transport layer, which possess higher hole mobility than the active polymer layer and which changes the height of the potential barrier at the interface transport layer/hole injection contact [81],... 

One has to consider that in Eqs. (9.15)—(9.17) the mobility /t occurs as a parameter. As it will be pointed out below, // shows a characteristic dependence on the applied electric field typical for the type of organic material and for its intrinsic charge transport mechanisms. For the hole mobility, //, Blom et al. obtained a similar log///,( ) const. [E dependency [88, 891 from their device modeling for dialkoxy PPV as it is often observed for organic semiconductors (see below). 

Figure 12-28. Temperature dependence Figure 12-29. I hotocurrem transient of the 11X3/ of the hole mobility in DPOP-l PV MeLPPP/AI sample after excitation through the ITO ati-...

Figure 12-30. The electric field dependence of the hole mobility in McLPPP ut different lem-peralures.

The high electrical conductivity of metals as well as the high electron (and hole) mobility of inorganic covalently bound semiconductors have both been clarified by the band theory [I9, which slates that the discrele energy levels of individual atoms widen in the solid stale into alternatively allowed and forbidden bands. The... 

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