Expression for Multiplication

An avalanche photodiode composed of a p+-i-n+ multiplication region extending from x = 0 to x = Lm and a depletion region extending to x = wj is considered and modeled as shown in Fig. 9.4. The stack of multiple layers with p+-i-n+-n~-n+ (substrate) impurity doping profile is shown in Fig. 9.4(a) and (b). The electric field distribution when a reverse bias is applied to the device is drawn in Fig. 9.4(c). Figure 9.4(d) indicates

Fig. 9.4 Simplified model of avalanche photodiode: (a) structural concept by stack of multiple layers, (b) image of the doping profile, (c) image of electric field, and (d) schematic diagram of avalanche multiplication region. (The electric field is applied between x = 0 to Lm. Definition of direction of electric field and electron and hole currents are also defined.)

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