Short answers, pulled from the story.
A semiconductor is a material with electrical conductivity between that of a conductor and an insulator. Its conductivity can be modified by adding impurities, called doping, to its crystal structure. The behavior of charge carriers, including electrons, ions, and electron holes, at semiconductor junctions is the basis of diodes, transistors, and most modern electronics.
Common semiconductors include silicon, germanium, and gallium arsenide, along with elements near the metalloid staircase on the periodic table. After silicon, gallium arsenide is the second-most common semiconductor, used in laser diodes, solar cells, and microwave-frequency integrated circuits. Silicon and germanium both sit in group 14 and carry four valence electrons.
N-type doping uses Group V donor elements such as phosphorus, antimony, or arsenic to create free electrons. P-type doping uses Group III acceptor elements such as boron, gallium, or indium to create free holes. The labels indicate which charge carrier is the majority carrier in the material.
The first working transistor was a point-contact transistor invented by John Bardeen, Walter Houser Brattain, and William Shockley at Bell Labs in 1947. In 1954, physical chemist Morris Tanenbaum fabricated the first silicon junction transistor at Bell Labs. The integrated circuit followed in 1958.
Crystal ingots between 100 and 300 millimeters in diameter are grown as cylinders, usually by the Czochralski method, and sliced into round wafers. Processing includes thermal oxidation, photolithography with ultraviolet light, plasma etching, and diffusion doping in a 1,100 degree Celsius chamber. Silicon wafers were first introduced in the 1940s.
Heating a semiconductor provides energy that promotes electrons across the band gap, creating partially filled states in both the valence and conduction bands. This raises conductivity, the opposite of a metal, whose conductivity decreases as temperature rises. An intrinsic semiconductor has a smaller band gap than an insulator, so at room temperature many electrons can already cross it.