Can Doping Transform Any Isolator into a Semiconductor?

[Quasi Particle]

Semiconductors and isolators are only different in that the energy gap of the former is smaller than 2eV, and of the latter it is larger. I can change the energy gap by doping - but can I make any isolator a semiconducter? What are the limitations?

 

[Barth]

You can not really "change the gap" by doping a cristal. When you dope the cristal, you introduce impurities in the lattice. These impurities creates localised states for the electrons, whose energy is inside the gap. So you don't change the gap, you only create disrete levels inside.

All author's don't really agree for the difference semiconductors/isolators. When you cite a limit a 2eV, it is a little bit arbitrary.
The difference is that in a isolator, the energy gap is many ordrer of magnifude above the thermal energy kT at room temperature ( 25meV) , so the thermal excitation of electron and hole is negligible. In other words, there is no charge carriers at room temperature.
Instead, an element whose gap Eg is smaller than -let's say- 100*kT ( which for the room temperature of 300 K, means Eg<2 eV), presents a non-negligible occupation of the conduction band states, and then behaves as a semiconductor.

In summary, if you want that your isolator becomes a semiconductor, you just have to put it in a oven.

And for the doping limitations, i can't tell you. If i understood well, there is different effects that can happen when you dope too much an element. The first is that in highly doped elements, the fermi level comes into the conduction band. Your element then begin to have a metal-like behaviour.
The others are more technoligic: the doping of a material is not a trivial operation. Doping by ionic implantation, for instance, can heavily damage the sample if the concentration of dopants is too high.

 

[charng]

I can confirm that the energy gap is the main factor that distinguishes semiconductors from isolators. The energy gap is the minimum amount of energy required for an electron to jump from the valence band to the conduction band. In semiconductors, the energy gap is smaller than 2eV, while in isolators, it is larger.

Doping is a process of introducing impurities into a material to alter its electrical properties. In semiconductors, doping can change the number of free electrons or holes, thus affecting its conductivity. However, the same cannot be said for isolators. While doping can decrease the energy gap in isolators, it cannot make them into semiconductors.

The limitations for turning an isolator into a semiconductor are primarily due to the material's intrinsic properties. The crystal structure, bonding, and electronic structure of an isolator are fundamentally different from that of a semiconductor. These differences cannot be overcome by doping alone.

In summary, while doping can change the energy gap in isolators, it cannot make them into semiconductors. The limitations lie in the material's intrinsic properties, such as its crystal structure and electronic properties. Therefore, it is not possible to turn any isolator into a semiconductor, and the two should be considered distinct materials with different properties.