Alloy-junction transistor

The germanium alloy-junction transistor, or alloy transistor, was an early type of <a href="/facts/Bipolar_junction_transistor/9BMcGv5Q">bipolar junction transistor</a>, developed at <a href="/facts/General_Electric/bBm5CzVY">General Electric</a> and <a href="/facts/RCA/NWyjNN6R">RCA</a> in 1951 as an improvement over the earlier <a href="/facts/Grown-junction_transistor/fPE2G3oc">grown-junction transistor</a>.
The usual construction of an alloy-junction transistor is a <a href="/facts/Germanium/wtoALHGs">germanium</a> crystal forming the base, with emitter and collector alloy beads fused on opposite sides. <a href="/facts/Indium/zRq3stVb">Indium</a> and <a href="/facts/Antimony/YsA7lVgT">antimony</a> were commonly used to form the alloy junctions on a bar of N-type germanium. The collector junction pellet would be about 50 mils (thousandths of an inch) in diameter, and the emitter pellet about 20 mils. The base region would be on the order of 1 mil (0.001 inches, 25 μm) thick. There were several types of improved alloy-junction transistors developed over the years that they were manufactured. 
All types of alloy-junction transistors became obsolete in the early 1960s, with the introduction of the <a href="/facts/Planar_transistor/eWMFFFWd">planar transistor</a> which could be mass-produced easily while alloy-junction transistors had to be made individually. The first germanium planar transistors had much worse characteristics than alloy-junction germanium transistors of the period, but they cost much less, and the characteristics of planar transistors improved very rapidly, quickly exceeding those of all earlier germanium transistors.

Alloy-junction transistor open-in-new

Alloy-junction transistor