*Question E6B07:
What causes a junction diode to fail from excessive current?*  

*Correct Answer is  B: Excessive junction temperature*  

### AI Response: (may contain errors)  

A junction diode can fail from excessive current primarily due to excessive junction temperature. Here's why:

1. **Correct Answer: Excessive junction temperature**  
   - When a diode conducts too much current, it generates heat. If the heat is not dissipated effectively, the temperature of the junction can rise to a level that damages the diode. This is because the materials in the diode can only withstand a certain temperature before they start to degrade or melt, leading to failure.

2. **Why the other choices are incorrect:**
   - **Excessive inverse voltage (Choice A):**  
     This refers to the voltage applied in the reverse direction. While excessive inverse voltage can cause a diode to fail, it is not related to excessive current. Instead, it leads to breakdown due to the electric field exceeding the material's breakdown voltage.
   - **Insufficient forward voltage (Choice C):**  
     This means the voltage is too low to forward-bias the diode properly. It does not cause failure from excessive current; rather, it prevents the diode from conducting.
   - **Charge carrier depletion (Choice D):**  
     This is not a failure mode due to excessive current. Charge carrier depletion refers to the reduction of available charge carriers in a semiconductor, which is a normal part of diode operation in reverse bias, not a failure mechanism.

3. **Useful Rule of Thumb:**
   - The power dissipated in a diode can be calculated as:  
     $$ P = I^2 \times R $$  
     where:
     - $P$ is the power (heat) dissipated in watts,
     - $I$ is the current through the diode in amperes,
     - $R$ is the resistance in ohms.

   - If the power dissipation exceeds the diode's thermal limits, it can lead to excessive junction temperature and failure. Always ensure that the diode is operated within its specified current and power ratings to prevent overheating.