Diodes Under Pressure
1. Understanding Reverse Bias
So, you’re curious about what happens when a diode gets “reverse biased”? Picture this: a diode is like a one-way street for electricity. It’s designed to let current flow easily in one direction (that’s “forward bias”), but it’s supposed to block it going the other way. “Reverse bias” is when you try to force the electricity to go down that one-way street the wrong way. It’s like trying to drive your car against traffic — things aren’t going to go smoothly!
Think of a diode as a gatekeeper. In forward bias, the gatekeeper says, “Come on in, the party’s this way!” But in reverse bias, the gatekeeper crosses their arms and says, “Nope, not today!” The semiconductor material inside the diode, specifically the p-type and n-type regions, respond differently depending on the voltage you apply. In forward bias, the depletion region shrinks allowing current to flow. In reverse bias, that depletion region widens.
This widening of the depletion region is key. The depletion region is an area devoid of free charge carriers (electrons and holes). When it expands, it becomes a bigger and bigger insulator. The bigger this region gets, the harder it is for current to flow backward through the diode. Ideally, no current should flow at all. But alas, life (and physics) isn’t always ideal!
It’s not a perfect block, mind you. A tiny, tiny amount of current, called “leakage current” or “reverse saturation current,” does manage to sneak through. We’re talking minuscule amounts, usually in the microampere or nanoampere range for most diodes. But it’s there, and it’s important to understand. Think of it as a few raindrops getting through a closed window — annoying, but usually not a big deal. But what happens when the storm gets really bad?