Question E6B10:
In Figure E6-2, which is the schematic symbol for a Schottky diode?  

Choices:  
A: 1  
B: 6  
C: 2  
D: 3    

Correct Answer is  B: 6  

The correct answer is B: 6.

Why 6 is correct:
- The Schottky diode symbol looks like a regular diode but with a distinctive “kinked” or bent cathode bar. This denotes the metal–semiconductor junction characteristic of a Schottky barrier diode.
- Schottky diodes are known for very low forward voltage and virtually no reverse-recovery charge, which is why they are common in RF mixers and detectors.

Why the other choices are incorrect:
- 1: Ordinary PN junction diode (plain straight cathode line). Not a Schottky.
- 2: Zener diode (cathode line has bent tips indicating breakdown behavior). Used for voltage reference, not a Schottky.
- 3: Tunnel diode (curved/concave cathode plate), indicating negative resistance behavior. Not a Schottky.

Useful rules of thumb:
- Forward drop:
  - Schottky: $V_F \approx 0.2$ to $0.4\ \text{V}$
  - Silicon PN: $V_F \approx 0.6$ to $0.7\ \text{V}$
- Reverse recovery:
  - Schottky: $t_{rr} \approx 0$ (negligible charge storage)
  - PN diode: finite $t_{rr}$ (slower at RF)
- Temperature coefficient of $V_F$:
  - Schottky: roughly $-1\ \text{mV}/^\circ\text{C}$ (less negative than silicon PN)
- Practical tip: For RF detection/mixing and high-speed switching, choose Schottky for lower loss and speed; for voltage references, use Zener.