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It took many years for all the preparatory work to be set in place and the team to be set up before the actual transistor invention or transistor discovery could be made.
The team that invented the transistor worked well together, and despite some initial set-backs they made quick progress.
The environment that Bell Labs had set up worked well and this provided the right atmosphere for the transistor invention.
First attempts at the transistor invention
The semiconductor group started work on one of Shockley's ideas. He had deduced that it might be possible to develop a form of semiconductor triode. He envisaged a structure of layers of p and n type silicon. The main current would be carried in one of the layers and the conductance of this layer would be controlled by an external field. This would vary the number of charge carriers (holes or electrons) available to carry the current. Essentially this idea was the field effect transistor which is in widespread use today.
To create the structure to try out this idea, Shockley used some thin films of silicon which had been made by deposition. This in itself was a new process which had only just been developed by another Bell employee named Teal.
Using the new structure, Shockley expected that there would be a significant change in conduction as the controlling field was altered. To his great disappointment the effect was not observed. Calculations and theories were checked and rechecked by other members of the group and no reason was found for its failure.
It was not until March 1946 that the problem was solved. Bardeen reasoned that the semiconductor surface trapped electrons which screened the main channel from the effects of the external field. Later Shockley said that this discovery was one of the most significant developments in the whole of the semiconductor programme.
Change of Direction
Supposedly beaten by the trapped electrons the group changed direction. They turned their attention to investigations around reversed biassed p-n junctions in an attempt to develop a new kind of lightning arrestor. Research revolved around three layer structures with one forward and one reverse biassed junction, and work progressed on this through most of 1947.
It was towards the end of that year that events started to look up for the group. In November a new recruit to the team came up with a crucial idea. Returning to their earlier work on field effect devices he suggested that if an electrolyte was placed between the control plate and the conduction channel then the screening effect of the trapped electrons might be overcome. A new experiment was set up and it was successful, if only to a limited degree. With a measure of success behind them the team found a new degree of motivation. In the days that followed a host of ideas for possible amplifying devices were discussed.
In early December, Bardeen and Brattain started to experiment with two closely spaced point contact junctions as a new idea for the transistor invention. They found that when they forward biassed one and reverse biassed the other, a small amount of gain was noticed.
Soon the team started some further experiments based around this idea, but initially they were not able to exploit the transistor effect properly. In one experiment an electrolyte was even placed around the sample, but with each new test they came a step closer to discovering the full transistor effect.
Finally they decided that it was necessary to place two diode junctions about 0.05 mm apart. This was achieved remarkably easily. A layer of gold was deposited onto a small wedge of perspex. Then a razor blade was used to cut a very thin slit in the gold right at the point of the wedge. Then the wedge was placed onto a layer of germanium under the force produced by a small spring. The collector and emitter were formed by the two gold contacts and the germanium layer was the base contact.
The idea was tried on 16th December 1947 and to their surprise it worked first time. The first point contact transistor had been made and the transistor had been invented.
Exactly a week later Shockley, Bardeen and Brattain found themselves demonstrating the new transistor invention to senior management at Bell. This heralded the beginning of the transistor age. However many more developments were needed before these devices could become an everyday reality.