Semiconductor Materials: Fill & Download for Free

I recall two items that were hyped quite a bit. In the end they weren’t “pure hype” in the vaporware sense, but they didn’t deliver what the tech tabloids predicted.Gallium Arsenide (GaAs)In the late 80s and early 90s quite a few respected sources reported that we were about to hit a wall wrt. transistor switching speed. Silicon processors would not be able to go to 1GHz clock speeds. Heck, even the legendary Cray-2 didn’t quite hit 250MHz.However, a better semiconductor material was on the horizon: gallium arsenide. It was already used for some switching applications and soon some fabrication difficulties would be eliminated for it to completely replace silicon. The Cray-3 would be the forerunner of a new breed of superfast digital machines.Instead, the one manufactured Cray-3 was arguably the last of a kind, and GaAs never became the mainstream semiconductor material.Fourth-generation (Programming) Languages (4GL)Around the same time, programming magazines were hyping the idea of code-less programming. No longer would we have to learn cryptic languages like C, Lisp, or SmallTalk-80. Instead software would be developed by domain experts that need not to learn programming disciplines. Fourth-generation languages would be as intuitive as English… nay… more intuitive!It didn’t really happen. Sure, some specialized systems allowed non-programmers to develop useful computational solutions and domain-specific languages augmented productivity in some areas, but all these decades traditional text-based (“third-generation”) programming languages have remained the mainstay of most software.

There is an extremely straightforward explanation for this. We have metals - the conductors of electricity and non-metals, which are the opposite. Semi-conductors are the elements which lie in-between.As seen in the above diagram, the semiconductors lie in an area between the metals and non-metals.Now, before we proceed to the heart of this question, we must understand why metals conduct electricity. Every atom has an outer band of electrons, known as the valence band. In metals, the electrons from this valence band are not confined to the atom and are free to move throughout the metal lattice. It is this "sea of electrons" which makes conduction possible. It is exactly the opposite in non-metals, where the electrons are held tightly.Semi-conductors act as non-metals at low temperatures - the electrons are trapped within the atom. As the temperature of the semi-conductor is increased, the electrons in the valence band gain sufficient energy to escape from the confines of their atoms. As a result, in higher temperatures, a semi-conductor's valence electrons are free = conduction results, resistivity decreases.We call the energy required for an electron to escape - the "band-gap" of a semi-conductor.Higher the bandgap of a semi-conductor - more the energy needed to convert it into a conductor. The bandgap of Germanium is 0.67 eV, silicon at 1.1 eV. What can be deduced is that it takes a lower temperature to convert Germanium to a conductor than silicon.

A2A: It’s kinda true.The Molekule air filter uses small-scale semiconductors to oxidize organic molecules. The process is called “photoelectrochemical oxidation.” There’s a rather dense Wikipedia article on the subject. The short version is you use a semiconductor like titanium dioxide with semiconductor junctions on the order of the size of the molecules you want to oxidize. An incoming photon provides the energy to knock free an electron from the molecule you’re trying to oxidize. On one side of the semiconductor, you get an oxidation reaction; on the other, a reduction reaction, and Bob’s your uncle. All it takes is small enough areas of semiconductor material, which is where the “nanotechnology” and “molecular level” come from. (Though anything that breaks down pollutants does so at the molecular level, so whatever.)Yes, it’s reasonable to describe this as “nanotechnology,” strictly speaking, though it’s a bit overselling the case. It’s like calling your DVD player a quantum device because the laser inside it is a quantum well semiconductor—technically true, but more gee-whiz marketing than useful.What’s not clear to me is why you’d want to do this instead of just using a HEPA filter, which is cheaper and just as effective, only without nanotechnology woo. I suppose for certain kinds of applications it might be better, though none come to mind at the moment.