*Question E6A09:
What is a depletion-mode field-effect transistor (FET)?*  

*Correct Answer is  A: An FET that exhibits a current flow between source and drain when no gate voltage is applied*  

### AI Response: (may contain errors)  

A depletion-mode field-effect transistor (FET) is a type of FET that allows current to flow between the source and drain even when no voltage is applied to the gate. This is because the channel is already formed and conductive in its default state.

### Explanation of the Correct Answer:
- **Correct Answer (A)**: "An FET that exhibits a current flow between source and drain when no gate voltage is applied."
  - In a depletion-mode FET, the channel is normally "on," meaning that it conducts current without any gate voltage. When a negative gate voltage is applied, it depletes the channel of charge carriers, reducing the current flow.

### Explanation of Incorrect Answers:
- **Choice B**: "An FET that has no current flow between source and drain when no gate voltage is applied."
  - This describes an enhancement-mode FET, which is normally "off" and requires a positive gate voltage to create a conductive channel.

- **Choice C**: "An FET that exhibits very high electron mobility due to a lack of holes in the N-type material."
  - While electron mobility is a characteristic of FETs, this statement does not define a depletion-mode FET. It is more about the material properties rather than the operational mode of the FET.

- **Choice D**: "An FET for which holes are the majority carriers."
  - This describes a p-channel FET, not specifically a depletion-mode FET. Depletion-mode FETs can be either n-channel or p-channel, but the statement does not accurately define the operational characteristics of a depletion-mode FET.

### Summary:
- Depletion-mode FETs are conductive by default and require a negative gate voltage to reduce current flow.
- Enhancement-mode FETs are non-conductive by default and require a positive gate voltage to allow current flow. 

Understanding these distinctions is crucial for recognizing how different types of FETs operate in circuits.