# Understanding Diodes

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• August 3rd, 2017, 09:49 AM
Hazmatac
Understanding Diodes
So, I have a few topics I want clarification on. 1. What is up with reverse biasing? So, supposedly, if you hook up the negatively charged side of the silicone to the positively charged side of the battery, holes will flow into the battery from the silicone, widening the depletion region. Why are holes attracted to the battery though? What principle is at work there?2. As I understand the depletion region, it is a region where the p and n sides meet, and the extra electrons stuff the holes, creating a depletion region with no charge. However, I have watched a couple videos which seemed to suggest that there are ions in the depletion region, in other words, having a charge. What is the truth?3. How do minority carriers work?Thanks in advance :)
• August 3rd, 2017, 03:54 PM
tk421
Quote:

Originally Posted by Hazmatac
So, I have a few topics I want clarification on. 1. What is up with reverse biasing? So, supposedly, if you hook up the negatively charged side of the silicone to the positively charged side of the battery, holes will flow into the battery from the silicone, widening the depletion region. Why are holes attracted to the battery though? What principle is at work there?2. As I understand the depletion region, it is a region where the p and n sides meet, and the extra electrons stuff the holes, creating a depletion region with no charge. However, I have watched a couple videos which seemed to suggest that there are ions in the depletion region, in other words, having a charge. What is the truth?3. How do minority carriers work?Thanks in advance :)

It's extremely important to perform the bookkeeping correctly. In particular, one needs to track which charges are mobile, and which are not.

The depletion region earns its name from the fact that it is (largely) depleted of mobile charges. In an n-type region, the mobile carriers are n-type (electrons), so a depleted n-type region is free of mobile electrons, and thus has immobile positive charges (ions that were formerly mated to the electrons now on holiday).

When a battery is applied to a p-n junction diode, what happens depends on the polarity and magnitude of the connection. Just use "like charges repel, opposites attract" to deduce qualitatively what happens (again remembering that only some charges are mobile). If the polarity is such that the depletion zone increases in width, the diode is reverse-biased and negligible current results. If the polarity reduces the depletion zone's width, the diode is forward-biased and current increases. When the applied voltage is reasonably in excess of the thermal voltage (kT/q), then significant current will flow.