Diffusion voltage

Diffusion processes, in photography, 19 208 Diffusion theory, 23 101-107 Diffusion transfer reversal (DTR) processes, 19 273 black-and-white, 19 283 Diffusion voltage, 14 838... 

The diffusion voltage Vo and the barrier width W depend on the influence of diffusion and recombination (i. e. the Debye length Z-d = ]/D rrei, D = j = diffusion coefficient) and are therefore given by... 

Fig. 2. Formation of diffusion voltage Vj) in p—n junctions. Note Fm = macropotential which results from macroscopic space charges, double layers etc. Any shifting of Vyi caused by any kind of charge (positive charge in the n region and negative charge in the p region of p—n junctions) displaces the other energy levels in an analogous manner see 61> a) for details...

As with metal-semiconductor contacts, the electric field in the space charge, which is given by the diffusion voltage Fd and the width of the space-charge region W, separates optically generated electron-hole pairs. W is given by 41> ... 

Fig. 4. Scheme of the p—n photoefiect (according to S9>) explaining the generation of photo-emf. Note Ue = contact voltage between metal and photoconductor VD = diffusion voltage in the p—n junction Fph = reverse internal photo voltage (in relation to Vq)... 

Figure 2.6 Spatial dependence of excess carrier concentration Ap(x) for different diffusion voltages in the space charge region and for low excess carrier consumption at the surface (x = 0), expressed by...

The more strongly the mobilities of the two ions differ, the higher the diffusion voltage will be. Conversely, it disappears when the anions and cations possess equal mobility. This is a fact that can be utilized for practical applications, as we will see in the next chapter (Sect. 23.1). 

The two half-reactions can also be spatially separated from each other by dividing them into the two half-cells of a galvanic cell where they are connected to each other by an exterior circuit. For example, the so-called Daniell cell (Fig. 23.5) is composed of a Zn and a Cu electrode that are immersed in corresponding Zn " or Cu " solutions whereby these electrolyte solutions are in contact with each other through a diaphragm. To avoid diffusion voltages, a salt bridge can be used instead. 

E As diffusion voltage between measuring solution and solution inside the reference electrode. 

E as diffusion voltage is not described by the Nernst equation (Equ. 3). It is considerably dependent on the specific conditions and thus comprises a source of error. However, changes in the diffusion voltage usually only occur very slowly and can be taken into account by calibration. The quantity of Ez seldom exceeds a few mV. 

When the detector is illuminated, electron-hole pairs are created by photon absorption within the p-n junction. The electrons are driven by the diffusion voltage into the n-region, the holes into the p-region. This leads to a decrease A Vd of the diffusion voltage, which appears as the photovoltage Vph = AFd across the open electrodes of the photodiode. If these electrodes are connected through an Ampere-meter, the photoinduced current... 

Fig. 4.84a-c. Photovoltaic diode (a) schematic structure and (b) generation of an electron-hole pair by photon absorption within the p-n junction, (c) Reduction of the diffusion voltage Vb for an open circuit... 

Figure 4.95 a Current-voltage characteristics of a dark and an illuminated diode b diffusion voltage and photovoltage at the open ends and photocurrent in a shortened diode as a function of incident radiation power... 

Pinhole test tester coils scan the coating surface with a high diffusion voltage (JIS K 6766). 

In the non-illuminated diode the diffusion of electrons from the n region into the p region (and the opposite diffusion of the holes) generates a space charge, which results in the diffusion voltage Vp and a corresponding electric field across the p-n junction (Fig.4.83b). Note that this diffusion voltage cannot be detected across the electrodes of the diode, because it is just compensated by the contact potentials at the two ends of the diode. 

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