*Question E6E01:
Why is gallium arsenide (GaAs) useful for semiconductor devices operating at UHF and higher frequencies?*  

*Correct Answer is  B: Higher electron mobility*  

### AI Response: (may contain errors)  

Gallium arsenide (GaAs) is a semiconductor material that is particularly useful for devices operating at ultra-high frequencies (UHF) and higher. Here's why:

1. **Correct Answer: Higher electron mobility (B)**
   - **Higher Electron Mobility**: GaAs has higher electron mobility compared to silicon. This means that electrons can move more quickly through the material, which is crucial for high-frequency applications. Faster electron movement allows for quicker switching speeds and better performance at UHF and microwave frequencies.

2. **Why the Other Choices are Incorrect:**
   - **Higher Noise Figures (A)**: GaAs does not inherently have higher noise figures. In fact, it often has lower noise figures compared to silicon, making it advantageous for low-noise applications.
   - **Lower Junction Voltage Drop (C)**: GaAs typically has a higher junction voltage drop compared to silicon. This is not a characteristic that makes it suitable for high-frequency operation.
   - **Lower Transconductance (D)**: GaAs devices generally have higher transconductance, which is beneficial for amplifying signals at high frequencies. Lower transconductance would not be advantageous for UHF applications.

3. **Useful Concepts:**
   - **Electron Mobility**: The ability of electrons to move through a semiconductor material. Higher mobility allows for faster device operation.
   - **Frequency Performance**: Materials with higher electron mobility can operate effectively at higher frequencies, making them suitable for applications like RF amplifiers and oscillators.

In summary, the high electron mobility of GaAs is the key factor that makes it suitable for semiconductor devices operating at UHF and higher frequencies. This property allows for faster signal processing and better performance in high-frequency applications.