Recombination within the space charge region

Recombination within the space-charge region is a non-trivial problem to treat from a computational perspective [14]. The methodology of Sah, Noyce, and Shockley [229] has been used by several authors [219, 220, 223, 230-232], Figure 20 illustrates the sensitivity of the current-potential profiles at the semiconductor-electrolyte interface to this recombination mode [230]. 

Here it has been assumed that there is no recombination within the space charge region. Accordingly, all holes generated within the space region are transferred. The two components, /sc and /jjff add up to the total hole current... 

To quantitatively sense the dimension of dsc using the dielectric constant e = 11.68 and typical density of donor states Ad = 1017cm-3 of Si and assuming AEF = 0.5 eV, one obtains that dsc is in the order of 0.1 p,m. Within the space charge region where it is assumed that no recombination occurs, excitation of holes leads to the current... 

A system in which only majority carriers (electrons in n-type) carry the current, is frequently called a majority carrier device . On the other hand, if the barrier height at a semiconductor-metal junction reaches values close to the bandgap then, in principle, an electron transfer via the valence band is also possible, as illustrated in Fig. 2.8a. In this case holes are injected under forward bias which diffuse towards the bulk of the semiconductor where they recombine with electrons ( minority carrier device ). It is further assumed that the quasi-Fermi levels are constant across the space charge region i.e. the recombination within the space charge layer is negligible. In addition Boltzmann equilibrium exists so that we have according to Eqs. (1.57) and (1.58)... 

Bisquert et al. attacked the problem from a different point of view [157]. As already indicated in Eq. (11.19), an ideality factor m is frequently introduced if the slope of current-potential curves does not follow an ideal diffusion model. This has also been observed with some solid-state devices such as pn-junctions (see Section 2.3) and Schottky junctions (Section 2.2). This was interpreted by the recombination of electron and holes via interband recombination centers or trapping states within the space charge region or by electron transfer via interface states. According to these models, the ideality factor is expected to be between... 

Returning to the carrier collection problem, consider Fig. 18 for an n-semiconductor-electrolyte interface. As can be seen, the electron-hole pairs are optically generated, both in the field-free and in the space charge regions within the semiconductor. Recombination of these... 

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