What are the forward voltage drops for Germanium and Silicon diodes, and which type is more commonly used?

• A. Germanium diodes have a forward drop of 0.3 V; Silicon diodes have 0.7 V; Silicon diodes are more common.
• B. Germanium diodes have a forward drop of 0.7 V; Silicon diodes have 0.3 V; Germanium diodes are more common.
• C. Germanium diodes have a forward drop of 0.3 V; Silicon diodes have 0.7 V; Germanium diodes are more common.
• D. Germanium diodes have a forward drop of 0.5 V; Silicon diodes have 1.0 V; Silicon diodes are more common.

Answer: (A)

In forward bias, a diode needs a small threshold voltage before it conducts. Germanium diodes typically show about 0.3 V of forward drop, while silicon diodes require about 0.7 V. This difference comes from the materials’ bandgaps: germanium has a smaller bandgap, so carriers cross the junction with less energy, giving a lower forward drop. Despite that, germanium diodes leak more and are more temperature-sensitive, making them less reliable for many applications. Silicon diodes, with a larger bandgap, offer better leakage control, higher voltage ratings, and more consistent performance, which is why they dominate practical use.

So the commonly taught pairing is 0.3 V for germanium and 0.7 V for silicon, with silicon diodes being the more widely used type. The other options either swap the drops or give nonstandard values, which don’t align with typical diode behavior and common practice.