Why is doping bad?

Answer 1

Pure semiconductors are insulators at room temperature. Impurities must be added to imbalance the covalent bonds of the crystal structure to make them conduct. This process of adding impurities is called doping. Dopants are usually selected from the columns immediately left (P type dopants producing hole current carriers) and immediately right (N type dopants producing electron current carriers) of the column of semiconductors on the Periodic Table.

By varying the amount of dopant the resistivity of the semiconductor varies inversely.

By using opposite type dopants adjacent to each other a PN junction forms, which can be used to make diodes, transistors, etc.

By doping an area of the semiconductor, oxidizing the surface of that area and plating the oxide with metal a MOS capacitorcan be made.

Components are wired together to make a circuit by covering the chip with an insulator (typically an oxide or nitride), etching holes in the insulator to the component contacts, plating the chip with metal and etching away the metal where you don't want things connected.

Thus doping (and a few other process steps) allows you to create all electronic components except inductors (and those can either be connected externally or simulated with a circuit called a "gyrator" consisting of a capacitor and several opamps) needed to make monolithic ICs.