Dark conductivity temperature dependence

As is the case for the dark resistivity, the dependence of the sensitivity of the photoconductivity (defmed here as the ratio between light and dark conductivity) on the deposition parameters is far from clear-cut. Some observations can be made, however. The first (obvious) one is that for a high sensitivity, the dark resistivity must be high. Apart from this, there does seem to be a general trend (clear-cut in the triethanolamine and citrate baths and seen also by the lack of appreciable photoconductivity in the one low- (room-) temperature-deposited film reported [40]) of an increase in photosensitivity (due to decrease in light resistivity) with increasing deposition temperature. 

Fig. 37. Band edge profile of a (In,Mn)As/GaSb heterostmcture. Eq. E. and Ep denote band edges of conduction band, valence band, and Fermi level, respectively, (b) Temperature dependence of the magnetization observed during cooldown in the dark (open circles) and warmup (solid circles) under a fixed magnetic field of 0.02 T. The effect of light irradiation at 5 K is also shown by an arrow, (c) Magnetization curves at 5 K observed before (open circles) and after (solid circles) light irradiation. Solid line shows a theoretical curve, (d) Hall resistivity />Hall observed at 5 K before (dashed line) and after (solid line) light irradiation (Koshihara...

In the original studies of the S-W effect on undoped and doped a-Si H films, the principal characteristics of the S-W effect and the presence of metastable defects in a-Si H were established (Staebler and Wronski, 1977 Wronski, 1978 Staebler and Wronski, 1980). It was found that the large light-induced conductivity changes are a bulk phenomenon that occurs between what may be considered a thermally stable state A and a new metastable conductivity state B. State A is perfectly reproducible and is independent of previous exposures to light. It is obtained after the a-Si H film is annealed (in the dark) at temperatures above 150 C and then cooled to room temperature. The annealing time required for state A depends on the... 

Fig. 3. Temperature dependence of the dark conductivity for the two a-Si H films of Fig. 1. The A lines are for after annealing and the others for after optical exposure. The numbers indicate the exposure time in minutes. [From Staebler and Wronski (1980).]...

Figure 8.13 illustrates the response of this EW in terms of cyclic voltammetry. In the cathodic cycle the window is transparent (combination of WO3 in the pristine state and of fully lithiated LiyNi03) and in the anodic cycle the window becomes reflective (dark blue, lithiated LixW03). However, as in the previously discussed case of ECDs, the temperature-dependent conductivity of the electrolyte is of crucial importance for this EW, whose response becomes manifest only above 60°C, namely at temperatures higher than the crystalline to amorphous transition point. In fact, at this temperature the solid-state EW operates with a good transmittance variation (i.e. from 20% to 55%) and with an excellent cyclability (Figure 8.14). However, the response time is slow, thus confirming that more versatile windows require the relacement of PEO-based polymer electrolytes with electrically improved materials having fast ion transport at ambient and subambient temperatures [40].

Dark conductivities ap allow a number of conclusions [199, 200] and are thus measured first. Since Iq = a U a linear dependence (s 1) of the dark current Id on the voltage U indicates ohmic behavior, a superlinear dependence (s 2) the presence of space charge limited currents (SCLC). The constant a is directly proportional to the proportion of free to trapped charge carriers, the dielectrical constant of the sample, the electrical field constant and the mobihty of the charge carriers. Finally a is also determined by the cell geometry. As a is proportional to the mobility p of the charge carriers it is in certain cases possible to calculate p from the slope of the Id/U curve. The dark conductivity of an ohmic conductor varies with the temperature in an Arrhenius type fashion. The... 

In 2000, Balberg (2000) classified the electrical transport in PS by reanalyzing experimental data collected from various published papers about the temperature dependence of DC dark conductivity, according to Meyer-Neldel rule (MNR)... 

While the field-dependent hopping conductivity at low temperatures was always a challenge for theoretical description, the theories for the temperature dependence of the hopping conductivity at low electric fields were successfully developed for all transport regimes for the dark conductivity [28, 43], for the drift mobility [29], and for the photoconductivity [30]. In all these theories, hopping transitions of electrons between localised states in the exponential band-tails play a decisive role, as described above. 

The temperature dependence of steady state photocurrents in Ceo samples has been reported by a number of authors [9,12-15,19,20,26,28,31,35,37,39,41,43,45-47,51,53-55,57]. The magnitude and the details of this temperature dependence vary considerably among published studies. At room temperature, for example, measured values of the photo and dark conductivities cover the ranges 10 -10 (ficm) and 10 -10 (Dcm) , respectively. The large variations... 

Figure 9.3 Temperature dependence of the in situ photoconductance for two Ceo films, using white light intensity of 2 mW/cm. Films were grown on sapphire substrates held at approx. 200°C. Starting Qo powder for film A was dried for a longer period. Inset shows temperature dependence of the dark conductances. (Reproduced by permission of the American Physical Society from ref...

Figure 9.8. Temperature dependence of the photoconductance, at hv = 2.64 eV, in an oxygen-free (circles), partially (triangles) and fully (squares) contaminated by oxygen C film. Dark conductance is also shown (solid circles). (Reproduced by permission of the American Physical Society from ref 55.)...

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