He characterised the temperature dependence of the rate of diffusion by measuring the position of the p-n barrier using probes. His early work was published in 1952 and pointed out that p-n barriers could be formed by diffusing donor elements into p-type germanium or acceptor elements into n-type germanium.įuller’s work was carried out diffusing arsenic or antimony into p-type germanium doped with gallium and indium into n-type germanium. I suppose one has to consider the fact that many more important decisions had to be made at that time.” I wrote a letter up the line at the time to that effect, but it apparently didn't stir up matters. In doing so he created a body of knowledge on the diffusion of other donor and acceptor elements.įuller recalls advocating the value of diffusion in a memo dated 7 th March 1951: “ When we were first developing the diffusion method (1950), I got the feeling that the Labs was not fully appreciative of the possibilities and were slow in backing our work. We went into the diffusion of the Group III and Group V elements and we published papers on them.” “ This work on copper led to a search for other fast-diffusing agents and to an examination of diffusion in general. Fuller showed that the contaminant was copper which diffused rapidly throughout germanium converting it to p-type. After the War he returned to Bell but as a result of the reorganization of Bell’s materials research moved into semiconductors.įuller investigated impurity diffusion in semiconductors beginning with the “ thermal conversion” problem in germanium in which an unknown contamination of n-type germanium changed it to p-type on heating at over 500 oC. Calvin Fuller suggested that p-n junctions could be formed through diffusion in 1951.įuller was a polymer chemist seconded from Bell to support synthetic rubber research during World War II. The work was performed by measuring diffusion from very thin layers of these elements alloyed to the surface of the germanium.īardeen’s conceptual breakthrough anticipated Bell’s later work on diffusion from the gas phase and that of Philips and Mullard which utilised differential diffusion of a mixture of two elements alloyed to the surface of a germanium pellet.īardeen may be the most famous of the Bell alumni to propose a diffused transistor but not the first. ĭunlap showed that in germanium donor or n-type impurities such as arsenic or antimony diffuse much more rapidly than acceptor or p-type impurities such as aluminium, gallium and indium. When Hall and Dunlap published P-N Junctions by Impurity Diffusion they made it clear that they thought the mechanism was “ thermal diffusion,” a view subsequently disputed and resolved by John Saby in 1953. It was not initially clear if p-n junctions were being formed by an indium-germanium alloying process or by diffusion of the indium into the n-type germanium pellet. ĭunlap’s research was intended to support the General Electric alloy junction transistor developed by John Saby in which two indium dots were alloyed to either side of a small pellet of n-type germanium: on alloying the indium created p-type regions giving a PNP structure. He noted that the concept for differential diffusion arose from the work of Dunlap and Brown at General Electric who had presented their work on diffusion coefficients of n-type and p-type impurities in germanium at “ recent talks” and subsequently published. “ By successive diffusion (or simultaneous diffusion if the rates are appropriate) of n and p-type impurities one could make a layered structure of the NPN or PNP varieties.” He also suggested that the two additional layers might be formed either sequentially or simultaneously by exploiting differential rates of diffusion of n-type and p-type impurities:
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