Point Contact Transistors: More to the Point

In What’s the point?: The Point Contact transistor I discussed Shockley’s white paper on the theory of the Point Contact Transistor. Let’s look further into this early transistor design.

It is interesting to note that the first point contact transistor was created from the semiconductor germanium. Paper clips and razor blades were used to make the first transistor prototype1 .

So in 1947, John Bardeen and Walter Brattain, put together a few of these transistors and connected them with some other components to make an audio amplifier. They showed their audio amplifier to some chief executives at Bell Telephone Company. The executives were impressed because this device did not need time to “warm up” like the heaters in vacuum tube circuits. They saw the power of this new technology.

The Nobel Prize organization commented: This invention was the spark that ignited a huge research effort in solid state electronics. Bardeen and Brattain received the Nobel Prize in Physics, 1956, together with William Shockley, “for their researches on semiconductors and their discovery of the transistor effect.” Shockley had developed a so-called junction transistor, which was built on thin slices of different types of semiconductor material pressed together. The junction transistor was easier to understand theoretically, and could be manufactured more reliably.

In the image below, Shockley mentions Deathnium , a name given by early electronic engineers to a trap in semiconductors that reduced the lifetime of both electron and hole charge carriers.

In this image, Schockley showed a way in which the Deathnium recombination process can occur. He says that there is an imperfection of some sort in the crystal which is capable of trapping an electron. (Image courtesy of Reference 1)

In this image, Schockley showed a way in which the Deathnium recombination process can occur. He says that there is an imperfection of some sort in the crystal which is capable of trapping an electron. (Image courtesy of Reference 1)

In part (a) of the figure, Shockley shows the electron approaching this ‘imperfection’. Shockley goes on to describe the event1 :

Part (b) shows what happens after the electron is trapped. If a hole reaches the center while the electron -is trapped in it, the electron may easily jump into the hole. The center is then left in its original condition and is ready to recombine another electron-hole pair. Evidently, the reverse process can also go on and the center can generate hole-electron pairs by proceeding through the steps represented by (c), (d), and (e) in the figure. In (d) the deathnium center is supposed to have captured an electron, not an excess electron in this case but one from an electron-pair bond. As a result, a hole is created which diffuses away from the center. Subsequently, in (e) the electron jumps out of the deathnium center which is then returned to its original state and may create other electron-hole pairs or recombine them as the case may be. Conservation of energy is achieved in these processes by the simultaneous absorption or generation of photons and phonons.

My good friend, Arlie Stonestreet II, Chief Engineer with Ultra-ICE, sent me these following X-Ray images he captured of a point contact transistor he has in his collection. You can even see the port-hole where they would manually twiddle the point contact wires.

Check out some of the photos that Kirkwood Rough (He is a long-time Analog Engineer-extraordinaire, presently at Upstairs Amps. See his patents here) shared with Arlie from his collection. Most interesting are the transistor curves. Arlie tried to duplicate that on his transistor but couldn't get good readings….

Semiconductor amplification regarding the transistor action, with voltage, current and power gain, was experimentally observed by Bardeen and Brattain in n-type polycrystalline Germanium on December 16, 1947. This was the result of the strategically placed of gold-plated line contacts in nearby single crystal grains of the polycrystalline material.

Shive’s experiment at Bell Labs in 19482 showed the importance of the geometrical configuration in determining the extent of bulk transport. Shockley’s contribution of injection over a barrier, p-n junction theory and junction transistor theory outlined the mathematical description of Bardeen and Brattain’s previously disclosed transistor action by using a one-dimensional analysis.

The rest is history. More to come on this subject on Planet Analog in the future. We need to understand and never lose sight of our rich history of electronics in order to understand who we are and how we got here today, just as a family needs to know its ancestry history for their identity.


1 Transistor Electronics: Imperfections, Unipolar and Analog Transistors, W. SHOCKLEY, PROCEEDINGS OF THE I.R.E., 1952

2 More Things in Heaven and Earth: A Celebration of Physics at the Millennium

3 comments on “Point Contact Transistors: More to the Point

  1. Hooey0
    May 10, 2017

    Steve – Very interesting and informative post, as always.

    It brought back memories of my early days learning about transistors. When I was in college, it was all about tubes, and semiconductors were in their infancy. 

    I still have some CK722 PNP junction transistors that were packaged in a blue case. I wonder if they still function.

    Keep up the great work!

  2. Norberto
    May 11, 2017

    More more interesting discovery

  3. paul.justus
    May 12, 2017

    Thanks for this article!

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