Short answers, pulled from the story.
Michael Faraday reported in 1833 that the resistance of silver sulfide specimens decreases when they are heated. This observation contradicted the behavior of metallic substances like copper which lose conductivity as temperature rises.
The first working point-contact transistor was invented by John Bardeen, Walter Houser Brattain, and William Shockley at Bell Labs in 1947. They managed to amplify signals by twenty decibels or more using this device.
Adding just 0.001 percent of arsenic to a one cubic centimeter sample of pure germanium at twenty degrees Celsius donates an extra one hundred quadrillion free electrons. This increases electrical conductivity by factors of thousands or millions compared to the original ten billion free electrons and holes combined.
A silicon crystal doped with boron results in a p-type material while one doped with phosphorus becomes n-type. Group III elements function as acceptors creating electron holes whereas Group V elements act as donors creating extra free electrons.
Charles Fritts constructed a working solar cell in 1883 using a metal plate coated with selenium and a thin layer of gold. This device became commercially useful in photographic light meters during the 1930s.