*Question E6A03:
Why does a PN-junction diode not conduct current when reverse biased?*  

*Correct Answer is  C: Holes in P-type material and electrons in the N-type material are separated by the applied voltage, widening the depletion region*  

### AI Response: (may contain errors)  

A PN-junction diode consists of P-type and N-type semiconductor materials joined together. Here's why the diode does not conduct current when reverse biased:

### Correct Answer: C
- **Explanation**: When a diode is reverse biased, the external voltage is applied in such a way that it increases the potential barrier at the junction. This causes the holes in the P-type material and the electrons in the N-type material to be pulled away from the junction. As a result, the depletion region, which is the area around the junction devoid of charge carriers, becomes wider. This wider depletion region acts as an insulator, preventing current flow through the diode.

### Why Other Choices Are Incorrect:
- **Choice A**: "Only P-type semiconductor material can conduct current"  
  - **Incorrect**: Both P-type and N-type materials can conduct current. In a forward-biased diode, current flows due to the movement of holes in the P-type and electrons in the N-type material.

- **Choice B**: "Only N-type semiconductor material can conduct current"  
  - **Incorrect**: Similar to choice A, this is incorrect because both types of materials are capable of conducting current. The conduction depends on the biasing of the diode.

- **Choice D**: "Excess holes in P-type material combine with the electrons in N-type material, converting the entire diode into an insulator"  
  - **Incorrect**: This description is not accurate. The diode does not become an insulator due to the combination of holes and electrons. Instead, the widening of the depletion region due to reverse biasing is what prevents current flow.

### Key Concept:
- **Depletion Region**: The area around the PN junction that is void of free charge carriers. It acts as a barrier to current flow when the diode is reverse biased.

Understanding the behavior of the depletion region is crucial for grasping how diodes function under different biasing conditions.