What was the problem that the developers of the transistor were trying to solve?

Answer 1

To amplify an electrical signal you need a device that gives a voltage or current gain.

The crystal diode had been known about for 30 years before the invention of the thermionic diode and then triode by Lee de Forest. These glass tubes with glowing filaments and high voltages were fragile and wore out. In the 1950's the Bell lab scientists looked again at the crystal diode and worked with a bar of pure Germanium. They were able to push this semiconductor into being an insulator or good conductor by doping the Germanium with Indium or Arsenic. The doping gases made P or N type Germanium and by arranging a sandwich of PNP germanium with layers known as Collector,Base.and Emitter. The base region at the centre of the sandwich was made very thin indeed and was the point at with the low level signal was injected. The biasing of this base region with a small dc voltage could turn the Collector/Emitter into full conduction or,if lowered very slightly,into a near perfect insulator. With this small bias set to make the collector voltage just starting to fall an AC signal was superimposed on this steady dc bias. The signal on base now appeared at the collector,inverted and amplified by a significant amount. By feeding a fraction of the output back into the base a positive feedback loop was created and the first transistor phase shift sine wave oscillator was born. This point contact germanium transistor still exists and Bell scientists Bardeen,Brattain and Shockley got the Nobel Prize for it's invention.This invention paved the way for today's wired world and is the most significant invention of the 20th century.