According to Resnick, Walker & Halliday's Fundamentals of Physics (10th edition),
Figure 41-15 shows why a p-n junction operates as a junction rectifier. In Fig. 41-15a, a battery is connected across the junction with its positive terminal connected at the p side. In this forward-bias connection, the p side becomes more positive and the n side becomes more negative, thus decreasing the height of the potential barrier $V_0$ of Fig. 41-12c. More of the majority carriers can now surmount this smaller barrier; hence, the diffusion current $I_{diff}$ increases markedly.
The minority carriers that form the drift current, however, sense no barrier; so the drift current $I_{drift}$ is not affected by the external battery. The nice current balance that existed at zero bias (see Fig. 41-12d) is thus upset, and, as shown in Fig. 41-15a, a large net forward current IF appears in the circuit.
Another effect of forward bias is to narrow the depletion zone, as a comparison of Fig. 41-12b and Fig. 41-15a shows. The depletion zone narrows because the reduced potential barrier associated with forward bias must be associated with a smaller space charge. Because the ions producing the space charge are fixed in their lattice sites, a reduction in their number can come about only through a reduction in the width of the depletion zone.
Because the depletion zone normally contains very few charge carriers, it is normally a region of high resistivity. However, when its width is substantially reduced by a forward bias, its resistance is also reduced substantially, as is consistent with the large forward current.
My questions are as follows:
- According to the authors, the depletion zone becomes narrower when the diode is connected in forward bias because the height of the potential barrier, $V_0$, decreases. Height of $V_0$ decreases because the p-side is connected with the positive terminal of $V_{ext}$ and the n-side is connected with the negative terminal of $V_{ext}$, according to the authors. Can someone please explain more easily and clearly why the the height of the potential barrier, $V_0$, decreases when the diode is connected in forward-bias?
- If $V_{ext}$ is increased, will the depletion zone become narrower? Can $V_{ext}$ be increased so much that the depletion zone becomes non-existent? This question is a good segue to my 3rd question.
- Is the forward biasing voltage the cause of the dynamic resistance of the diode? If an AC source, $V_{{ext}_{ac}}$, is added with the DC source, $V_{ext}$, will the resistance of the diode vary with time? Is this resistance of the diode called the dynamic resistance?