Doping is when we add impurities to the extremely pure silicon. This changes the electrochemical properties of the silicon.
Silicon is in group 4 of the periodic table. Like Carbon it makes nice solid bonds in 4 directions. By adding elements from the 3rd or 5th columns we can add extra electrons or extra positive charges (holes where there are no electrons).
The elements we typically use are Boron for p-type (positive holes) doping and Phosphorus or Arsenic for n-type (extra electrons) doping. Undoped silicon has a very low conductivity meaning it does not conduct electricity, but it looks metallic. By adding small amounts of dopants it can be made to be conductive, and the voltage on transistor gates can change it from being insulating to conducting by controlling the way the extra (for N type) or missing (for P type) electrons behave.
The Arsenic is the poison in this fun tweet:
For more information check this article from technocrazed
The Zero To ASIC course took me on a fantastic journey from drawing and simulating a MOSFET, formal verification leading up to implementing a custom design with an open PDK and completely open source tools. The course is crammed full of interesting material with great pacing and support from Matt, and it's been a fantastic opportunity to meet other folks with shared interests and different backgrounds. The course has left me excited with opportunities for new projects and optimism for some working silicon!