Question

Why is a diode 0.7 V?

Answer 1

The 0.7V you're referring to is typically the forward voltage drop of a silicon diode. It’s the minimum voltage required for the diode to allow current to flow through it in the forward direction (from anode to cathode).

Here’s why this happens:

1. Material Properties: A diode is made from semiconductor materials like silicon. In silicon diodes, the energy required to move electrons across the junction (between the P-type and N-type materials) is about 0.7 volts. This is because of the way silicon atoms form bonds and the energy needed to overcome these bonds and allow current to flow.
   

1. Formation of a Depletion Region: When the P-type and N-type materials are brought together, they form a region called the depletion region. This region acts as a barrier to current flow. When a voltage is applied in the forward direction (positive on the anode, negative on the cathode), it needs to overcome the potential barrier in the depletion region.
   

1. Threshold Voltage: For a silicon diode, this barrier is about 0.7V. If you apply a voltage less than this (e.g., 0.5V), the diode won’t conduct because the barrier isn't fully overcome. Once the voltage exceeds 0.7V, the diode begins to conduct, allowing current to flow easily.
   

For other materials:

1. Germanium diodes typically have a lower forward voltage drop (about 0.3V) because germanium atoms have a lower bandgap compared to silicon.
   

  
So, in summary, the 0.7V is a characteristic of the energy required for the silicon material to overcome its internal barrier and allow current to flow in the forward direction.