Telefunken GC1

Footnote on the Telefunken GC1 Point Contact Transistor

Please return to the main article on the early history of Telefunken semiconductors.

The Telefunken GC1 is a very unusual point-contact transistor featuring:

(a) Gold whiskers

(b) Doping of the whiskers with N type impurity for the collector and P type for the emitter

Left: Front View Showing Bonded Electrodes: Right: Rear View

Left Telefunken GC1 Right: Wrapper showing Doping Levels

Courtesy Siegfried Neumann and Radiomuseum

The wrapper states that the collector whisker is 0.15mm antimony doped gold (N-type) and the emitter whisker gallium doped gold (P-type).

No further Telefunken information is available but publications from other laboratories do illustrate why this transistor is quite unusual and what the likely purpose was:

Gold Bonded Contacts

Normal point-contact transistors required the whisker to make a spring like connection to the transistor base in order to exert the modest force needed for a rectifying contact. Gold is too ductile to allow this but came into common use in “bonded” gold diodes made in large quantities in the USA, for example. Bonding was a process where a rugged gold-germanium alloyed contact was made by passing a DC current through the contact sufficient to heat it to the gold-germanium eutectic (358^oC) fusing the whisker to the base.

Thus the use of gold suggests that the GC1 had bonded whiskers.

Formed Point Contacts

The conventional forming process using phosphor-bronze, copper, tungsten or ruthenium whiskers achieved the desired effect by thermal treatment through electrical heating of the immediate environs of the contact.

In 1950 Bardeen and Pfann summarised work at Bell Laboratories in the previous year reporting that the performance of N-type point-contact transistors could be improved by passing large reverse currents through the collector contact. Conversely P-type transistors could be improved by passing a large forward current through the emitter. They suggested that the effect was due to migration of donor or acceptor ions from the body germanium to the surface modifying the rectifying barrier at the point-contact junction. [Bardeen 1950]

A year later Pfann revised this view proposing that forming could involve the migration of donors or acceptors from the metal contact demonstrating the effect by using formed collectors with a range of low levels of antimony in N-type germanium transistors. He showed that increasing the antimony content improved the current gain of the transistor. [Pfann 1951]

Similarly the GC1 had a antimony doped collector.

At RCA Stelmak produced similar results for formed phosphor bronze collectors containing varying levels of phosphorous. His results were more quantitative showing forming produced power gains of an additional 10 db with up to 0.1% phosphorous (over “pure” copper). [Stelmak 1951]

Much later than the date of the GC1, researchers at the Radar Research Establishment in Britain experimented with silicon point contact transistors in which both the emitter and collector were doped. For example they made formed point-contact transistors using a N-type silicon base and the same doping regime as the GC1:

(a) Collectors with whisker materials containing phosphorous, arsenic or antimony (N-type); and

(b) Emitters with whisker materials containing aluminium, indium or gallium (P-Type)

The work was directed to silicon transistors with improved power gains and saturation output characteristics for use in trigger circuits but the authors found that forming both collector and emitter was not essential. [Granville 1955]

This data suggests the GC1 was in development by Telefunken for switching applications.

References

Bardeen J Pfann W 1950 Effects of electrical forming on rectifying barriers of n- and p-germanium transistors Phys. Rev 77 401-2

Granville W Bardsley W Gibbon 1955 A Forming Procedures for Silicon Point-contact Transistors Brit Jnl Appl Phys 6 206-10

Pfann W 1951 Significance of Composition of Contact Point in Rectifying Junctions on Germanium Phys. Rev.81 882

Stelmak J 1951 Electric Forming in n-Germanium Transistors Using Phosphorous Alloy Contacts Phys Rev 83 165