Depletion Layer and an Air Gap

It is interesting to consider the differences and similarities between the depletion layer or transition layer in a semiconductor and an air gap. This is important because for decades the mechanical relay used an air gap to produce an 'open circuit' output that would break the circuit and inhibit current flow. Now semiconductors can do the same thing using the depletion layer but exploring this part of a semiconductor takes a bit more imagination.

Imagination is needed because there aren't great descriptions of how the depletion layer works beyond a smoothing of the charge balances between 'positive' and 'negative' doped semiconductor regions. How do those charges jump around? Like the charge discussed in my posts on gravity, the depletion layer may see spark-like charge jumps and fuzzy-Gaussian charge movement akin to the boil seen in a kettle.

The spark-like carriers I write about are often termed hot carriers and although the Poisson - Gaussian statistical movements are not termed cool carriers, The term shot is often used in noise theory and has also been related to the Poisson arrivals in mathematics. Thinking hard about what electrons are doing statistically leads quickly to words like fuzzy vs. spiky.

Let us consider, more closely, the depletion layer of a standard Si diode that does not have Schottkey properties. The standard theory states that there is charge smoothing through the depletion layer. Doped Si on either side of of the p-n junction swaps sides causing the depletion layer to exhibit a neutral or opposing charge.

I'd like to see more research in this area of Poisson vs. Gauss statistics in the p-n junction. How does 1/f noise factor into the analysis? The p-n junction may have a kettle boil of charge that traverses the junction with a statistical equilibrium that causes the diode action. The incoming charge comes in hot and crosses the diode to the junction where it either piles on to the depletion layer or in fires right through relatively hot (though nothing like the Schottkey diode). Diodes behave differently depending on whether or not they are forward or reverse biased.

A full comparison to the air gap in a relay will have to wait for a future blog post. It is enough to say, right now, that when the incoming carriers pile into the diode they are under what people our size might term - incredible pressure. At the electron feature size particles behave differently. The growth of the depletion layer due to incoming carriers leads to what I would estimate is a Gaussian or fuzzy electron distribution. This kettle boil keeps the reversed biased diode 'gaped from conduction'. The depletion layer is not an air gap where arcs are prevented. The depletion layer provides a push back that mimics the air gap of an electro-mechanical relay.