During what bias does a cathode have a more positive charge than an anode?

In a semiconductor context, the correct condition is reverse bias. When a diode is in reverse bias, the anode is at a higher potential compared to the cathode, meaning that the cathode experiences a more positive charge relative to the anode. This situation results in minimal current flow across the diode, as the reverse bias widens the depletion region, preventing charge carriers from crossing the junction.

In scenarios such as forward bias, the anode is made more positive than the cathode, allowing current to flow freely. Zero bias refers to when no external voltage is applied, resulting in negligible charge difference between the electrodes. Breakdown bias refers to the condition where the reverse voltage reaches a point that allows current to flow again, but in this state, the anode is not more positive than the cathode. Thus, recognizing that the reverse bias condition specifically entails the cathode being more positively charged than the anode clarifies why that option is the correct answer.