Mobility carrier density

The main variables that determine the transport and screening (see below) of both intrinsic and extrinsic semiconductors are the mobile carrier densities n and 7A, Given the energetic information, that is, the electronic band structure, and the dopant concentrations, these densities can be evaluated from equilibrium statistical mechanics. For example, the density of electrons in the conduction band is... 

Xia Y, Cho JH, Lee J, Ruden PP, Frisbie CD (2009) Comparison of the mobility-carrier density relation in polymer and single-crystal organic transistors employing vacuum and liquid gate dielectrics. Adv Mater 21 2174—2179... 

Another issue that can be clarified with the aid of numerical simulations is that of the recombination profile. Mailiaras and Scott [145] have found that recombination takes place closer to the contact that injects the less mobile carrier, regardless of the injection characteristics. In Figure 13-12, the calculated recombination profiles arc shown for an OLED with an ohmic anode and an injection-limited cathode. When the two carriers have equal mobilities, despite the fact that the hole density is substantially larger than the electron density, electrons make it all the way to the anode and the recombination profile is uniform throughout the sample. 

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 excellent agreement between the TSC and P1A results has two implications. First, since the TSC method probes the product of mobility and carrier density, while the P1A probes only the carrier density, there seems to be no dominant influence of temperature on the carrier mobility. This was also found in other conjugated polymers like /ra/ry-polyacetylene [19, 36]. Second, photoconductivity (observed via the thermal release of photoexcited and trapped earners) and photo-induced absorption probe the same charged entity [36, 37J. 

In the study by Johnson et al. (1986) it was shown by Hall effect measurements that the sheet carrier density was decreased and the mobility was increased for a thin w-type layer following exposure to a hydrogen plasma at 150°C. To explain the mobility increase it was argued that donor-H complexes were formed and that the concentration of ionized scattering centers was thereby decreased. On the basis of semiempirical calculations, a structural model was suggested for the donor-H complex in... 

L.-S. Yu and S.A. Chen, Full-range tunability of electron and hole carrier mobilities and density ratios via incorporation of highly electron-deficient moieties in poly(phenylene vinylene) side chains, Adv. Mater., 16 744-748, 2004. 

Fig. 8 Temperature dependence of the zero field hole mobility in the low carrier density limit in a polyfluorene copolymer. The data are inferred from space-charge-limited current experiments and analyzed in terms of the extended Gaussian disorder model (see Sect. 4.1). From [90] with permission. Copyright (2008) by the American Institute of Physics...

Zhou J, Zhou YC, Zhao JM, Wu CQ, Ding XM, Hou XY (2007) Carrier density dependence of mobility in organic solids a Monte Carlo simulation. Phys Rev B 75 153201... 

Doping a p-type semiconductor generates fixed acceptor sites with a density Na, and an equal number of mobile carriers with an opposite charge h+, whose distribution is controlled by the local value of the potential T>(x), following the Boltzmann function so that the mobile charge distribution is given by ... 

This Eq. (13) is derived from the fundamental electrochemical kinetics at metal electrodes and mainly accounts for the mechanism of the transformation, but the Gerischer Eq. (10) introduces an additional term accounting for the density of available mobile carriers at the electrode surface. 

The doping level of the silicon substrate is a determining parameter for the density of mobile carriers at the interface, even when the electrode is in the accumulation regime. Zhang [6] determined the cathodic current/voltage graphs for an n-type sample doped 10 and 10 ... 

On lowering the temperature through Ty, a bandgap Eg = 0.1 eV appears in the FeB-ai(l) conduction band of Fig. 3 at Ep. The Hall coefficient increases as Rh exp(Ty/T), indicating that the charge-carrier density increases exponentially with T" , as in a normal semiconductor, and the Hall mobility increases from about 0.1 to 0.4 cm /Vs on lowering the temperature from Ty = 120 K to 77 K ... 

The Hall effect, an electric field perpendicular to both the impressed current flow and to the applied magnetic field, gives information about the mobility of the charge carriers as well as their sign. The Hall coefficient RH - Ey/JxHe is proportional to the reciprocal of the carrier density. The Hall coefficient is negative for electron charge carriers. 

The mobilities of holes are always less than those of electrons that is fXh < Me- In silicon and germanium, the ratio [ie/[ih is approximately three and two, respectively (see Table 6.2). Since the mobilities change only slightly as compared to the change of the charge carrier densities with temperature, the temperature variation of conductivity for an intrinsic semiconductor is similar to that of charge carrier density. 

Neglecting the variation of the term, which is negligible compared to the variation with temperature in the exponential term, and recalling that the mobilities are less sensitive to temperature than are the charge carrier densities, Eq. (6.30) can be rewritten as... 

Unlike intrinsic semiconductors, in which the conductivity is dominated by the exponential temperature aud band-gap expression of Eq. (6.31), the conductivity of extrinsic semiconductors is governed by competing forces charge carrier density and charge carrier mobility. At low temperatures, the number of charge carriers initially... 

In a similar study, the deposition conditions were modified [pH of 8 (by ammonia), no Ag catalyst, and a deposition temperatnre of 80°C] [30], A primary thin film was deposited, followed by a second deposition, resnlting in films several microns thick. Optical absorption spectroscopy gave abandgap of 1.7 eV. The film resistivity was 1.3 X 10 ft-cm (carrier density = 8 X 10 cm mobility = 50 cm V sec ). 

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