Grown-junction transistor

An NPN grown-junction transistor is made of a single crystal of semiconductor material which has two PN junctions grown into it.

To facilitate this operation, the gold wire is pointed or flattened until the end is thinner than the base layer.

The tip of the gold wire is slid along the bar until electrical resistance measurement shows it is in contact with the base layer.

To avoid shorting the transistor, the gold wire is alloyed with a small amount of the same type dopant as used in the base.

Grown-junction transistors rarely operated at frequencies above the audio range, due to their relatively thick base layers.