Engineering Physics

8.9 Continuity equation

The mathematical relations formed from the excess carriers in unit volume of semiconductor due to generation, recombination, drift and diffusion are called continuity equations. The continuity equation can be derived with reference to an elemental volume A δx at x in a rectangular bar of semiconductor is shown in Fig. 8.10.

Let the number of excess electrons in the element due to generation, recombination, drift and diffusion is ∆n (Aδx) and the rate of increase of this number in the element is:

 

Figure 8.10 A rectangular bar of semiconductor

This value can be extracted separately in the following way:

(a) Rate of ...