wjfox: Why is a semiconductor called a "semi" conductor, and not just a conductor?
GPT-4: Semiconductors are so named because their ability to conduct electricity falls somewhere between that of insulators, which do not conduct electricity well, and conductors, which do so freely.
In more technical terms, a semiconductor is a material that has an electrical conductivity value falling between that of a conductor, like copper, and an insulator, like glass. This middle ground is due to the presence of the so-called "energy band gap." In solid state physics, the band gap of a solid substance represents the energy difference (in electron volts) between the top of the valence band and the bottom of the conduction band in insulators and semiconductors. It's a sort of energy barrier that must be overcome for an electron to participate in electrical conduction.
In conductors, the valence and conduction bands overlap, meaning that there are always some electrons in the conduction band, which allows the material to conduct electric current. On the other hand, insulators have a very large band gap, which makes it very difficult for the electrons to jump from the valence to the conduction band, therefore inhibiting conductivity.
Semiconductors are unique because their band gap isn't as large as insulators but also isn't nonexistent like in conductors. It's a middle-ground scenario, hence the term "semi" conductor. This characteristic makes them very important in electronics because we can manipulate their conductivity. By adding impurities, a process called doping, we can control the number of free charges and therefore control the current, making semiconductors very useful for devices like transistors and diodes.
Today I Learned
Re: Today I Learned
To know is essentially the same as not knowing. The only thing that occurs is the rearrangement of atoms in your brain.
Re: Today I Learned
My memories of watching "Finding Nemo" has been utterly destroyed. 
To know is essentially the same as not knowing. The only thing that occurs is the rearrangement of atoms in your brain.
Re: Today I Learned
I'm never seeing seagulls in the same way again.
To know is essentially the same as not knowing. The only thing that occurs is the rearrangement of atoms in your brain.
Re: Today I Learned
Crabs can fly underwater. 
To know is essentially the same as not knowing. The only thing that occurs is the rearrangement of atoms in your brain.
Re: Today I Learned
To know is essentially the same as not knowing. The only thing that occurs is the rearrangement of atoms in your brain.
