Saturation, current density

The reciprocal derivatives of the j/V curve under illumination at open circuit and short circuit represent the series and parallel resistances Rs and Rp, respectively, of the diode device. Of course, for non-linear effects in the diode, these quantities are not constant but depend on voltage V, current density j (illumination level), reverse saturation current density jtev, and temperature T. 

Here Jo is the dark saturation current density, Rs is the series resistance, A is the area and Rp is the shunt resistance. When a voltage V exists on the junction, the output current of the illuminated solar cell has two components, (1) the junction current density 7j (illumination) due to injection of carriers and (2) the short circuit current density Jsc due to light generated carriers. Therefore the output current density J v of the illuminated solar cell is given by,... 

Fig. 9.3. Electrical characteristics of a palladium/a-Si H Schottky barrier (a) the exponential forward current, the ideality factor, n, the reverse current, and the effects of annealing, described in Section 9.1.3 (6) the temperature dependence of the saturation current density plotted according to Eq. (9.14) (Thompson et at. 1981).

The temperature dependence of J, measured by extrapolation of the forward J-V data, is shown is Fig. 9.3. The saturation current density is given in the thermionic emission model by... 

The data of Efimov and Erusalimchik (5) shown in Fig.l give an example of the different current-voltage characteristics obtained with various resistivity n- and p-type germanium electrodes made anode in 0.1 N HC1. Brattain and Garrett (4) and others (7-10), however, found much lower saturation current densities by one to two orders of magnitude with n-type germanium made anode in similar electrolytes. Similar curves for n-type silicon would show saturation current densities in the order of microamperes per square centimeter. 

The equilibrium hole concentration can be increased by raising the temperature of the semiconductor. Uhlir (7) found that the temperature variation of the saturation current density across the barrier between anodic n-type germanium and 10% potassium hydroxide solution is quite like that of a p-n junction. About a tenfold increase in the saturation current density is obtained for each 30° C rise in temperature as shown in Fig. 2. 

An extrapolation of the linear semilog plot to 100°C gives a maximum saturation current density of about 100 ma/cm2 which is sufficient for only a moderate etching rate. The increase in saturation current density with temperature for silicon is much less, since silicon has a larger energy gap than germanium. 

For thermionic emission from a uniform surface, the saturation current density j extrapolated to zero applied field is given by... 

In the experiment the forward saturation current density J t o r under the electron rich and diffusion conditions of the unignited mode, was 20 times larger than the value expected by the theory. This inexplicable results should be examined by another experiment. Also, what extent the V b could be reduced by T c optimization and what the maximum endurance temperature of the AgO x collector could be, should be examined further. 

Finally, fK is defined in terms of the average current density and the average saturation current density by the equation... 

In 1983 the application of doped tin oxide films to silicon solar cells has been reported [5]. lida and coworkers realized a setup with the following characteristics 7sc = 14 mAcm", Kic = 800 mV, efficiency = 7.5 % and fill factor = 0.67. Vishwakarma et al. [166, 167] prepared arsenic-doped tin oxide films for silicon solar cells and investigated the diode properties of Sn02 As/Si02/n-Si and Sn02 As/n-Si cells. The barrier height 0 was 0.78-0.89 eV and 0.68-0.69 eV, respectively, and the reverse saturation current density 7u was 2-45 pAcm and 0.07-9.2 pAcm", respectively, with diode quality factors of 2.2-2.9 and 1.7-1.9. The optimized results for solar cell applications are given below... 

SiC p-n diodes clearly illustrate the advantages of wide bandgap semiconductors in general and SiC in particular. The elementary theory of p-n junctions yields the following expression for the reverse saturation current density, JR, for a p+-n junction [1] ... 

Sommerfeld Formula for Thermionic Emission. Using the Sommerfeld formula (2-100), calculate the saturation current densities of thermionic emission for a tungsten cathode at 2500 K. Compare the calculated value of cathode current density with a typical value for the hot thermionic cathodes presented in Table 2-12. 

In addition, the ideality factor (n) and saturation current density (Jo) also improved significantly. The variation of the efficiency with the work function of the Schottky metal is important for films fabricated with STA, as shown in Figure 5.26. This variation is very small for films fabricated without STA. This is an... 

Here, O is the incident light flux, a is the absorption coefficient (assuming monochromatic illumination), W is the depletion layer width, Lp is the hole diffusion length, and jo is the saturation current density. The model assumes that there is no recombination in the SCR and at the interface. 

Jp and Jq are forward bias and reverse saturation current densities... 

The effect of the presence of a thin interfacial oxide on the dark current voltage characteristics of an SBSC has been examined in sections 2.2 and for the min MIS cell in 2.5. The exact role of the interfacial oxide is not fully understood at present, although it is known that both minority and majority carrier flow over the barrier decrease with increasing oxide thickness. If the oxide is sufficiently thick so that its transmission coefficient is no longer unity, the reverse saturation current density obtained from the forward vs V, characteristics is reduced causing an increase in the effective barrier height < ) This effect is... 

In a photodiode with Auger suppression the saturation current density decreases with reverse bias, thus leading to the appearance of negative differential resistance. For the above described case we calculate this current according to... 

Fig. 3.29 Saturation current density versus operating temperature for various compositions of the active area in a mercury cadmium telluride extraction photodiode limited by radiative processes. The active region width w = 2 pm...

---