Alloy-junction transistor

The usual construction of an alloy-junction transistor is a germanium crystal forming the base, with emitter and collector alloy beads fused on opposite sides.

Indium and antimony were commonly used to form the alloy junctions on a bar of N-type germanium.

It is constructed of a semiconductor crystal forming the base, into which a pair of wells are etched (similar to Philco's earlier surface-barrier transistor) on opposite sides then fusing emitter and collector alloy beads into the wells.

The post-alloy diffused transistor solved this problem by making the bulk semiconductor crystal the collector (instead of the base), which could be as thick as necessary for mechanical strength.

Then two alloy beads, one P-type and one N-type were fused on top of the diffused base layer.