Bulk Fermi level

Fig. 8.14. Theoretical plots showing competition between recombination and current doubling. Calculated for a surface state density of 5 x 10,2cm "2. The surface state is located 0.3eV below the bulk Fermi level. Donor density 1.5 x I0,ftcm. Arinj 5 x 104s" rccn = 2 x 10 7 s. Band bending values (a) 0.40 eV, (b) 0.35 eV, (c) 0.30 eV, (d) 0.2 eV. Note the transition in the IMPS response from current from current doubling control at 0.4 eV to...

Fig. 16. Principles of the photovoltage measurement, (a) Semiconductor in the dark, with the bulk Fermi level E in equilibrium with P ,dol( (b) under illumination, when the open-circuit potential adjusts so that, in principle, there is no potential drop in the depletion layer.

The difference between the flatband potentials ofp-Si and n-Si plus the differences between the bulk Fermi level to the corresponding band edges equal the band gap, 1.12eV when the band edges of the two materials are the same in the solution. Such situations have been observed." " However, in many situations the measurement of flatband potentials ofp-Si and n-Si does not yield the band gap. There are two possible explanations. In one the band edges of p -Si and n-Si may not have the same energy... 

Thermal equilibrium requires that the capture rate equal the emission rate at Ef. Therefore, majority-carrier capture follows the same dependence on energy and temperature as Eq. (5). However, for capture the characteristic energy E denotes the height of the conduction-band edge above the bulk Fermi level, E = AEp -b w(x), where AEp = E — Ep in the bulk material. This energy is the average energy of the potentid barrier that electrons must travel up to be captured at the point x under consideration. 

Fig. 30. In (a) the 10-kHz capacitance versus temperature is displayed for the 2 densities of states shown in Fig. 20 as well as a constant g(E) = lO cm eV [as indicated by the dashed and dotted (as in Fig. 20) and dash-dotted lines, respectively] at which now the bulk Fermi level E% is assumed to lie 0.6 eV below E. In (b) the ratio C [dCldT] is plotted versus temperature. As explained in the text, the slope and curvature of these curves are directly related to the value and slope, respectively, oig(E) at FJ.

Fio. 52. Summary of the density-of-states results for five different a-Si H films with differing amounts of phosphorus doping (see description in text). The films have slightly different deduced band gaps, and for purposes of comparison the curves are all normalized to the conduction-band (mobility) edge E. The position of the bulk Fermi level in each film is indicated. [From Lang et at. (1982a).]... 

Here, o and po are the equilibrium carrier concentrations in the dark, and An and Ap are the additional carriers created by iUuminatiOTi. For an n-type semiconductor, n = o+An Wq and p = po+Ap Ap so that remains horizontal whereas departs from the bulk Fermi level in the active region. 

Surfaces and interfaces break the periodicity of the ideal crystal. This can be taken into account by introducing surface (interface) electronic levels in the forbidden gap, of density of states Ns(E). The filling of these specific states defines a Fermi Ep level different from the bulk Fermi level Ep. 

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