Bidirectional transistor

DETAILED DESCRIPTION It is an object of the present invention to provide a semiconductor device having greatly improved bidirectional characteristics, including a very substantial increase in the current gain factor.
More specifically, this invention relates to a bidirectional transistor, and particularly to a transistor having two low impurity concentration regions on either side of a base region which act as the emitter or collector regions with a minority carrier diffusion length L substantially greater than the width of such emitter and collector regions when operating in either direction.
High impurity concentration regions interface with the low impurity concentration regions to provide a built-in-field which is larger than kT/(qL) and which make the drift current produced by the built-in-field substantially balance the minority carrier diffusion current injected from the base region.
The built-in-field is preferably larger than 10.
sup.
3 V/cm, and the potential barrier across is preferably larger than 0.
1 eV.
Two of the high impurity concentration regions provide first and second L-H junctions.
A third L-H junction surrounds one of the low impurity concentration regions.
This third L-H junction greatly improves the bidirectional characteristics of the device.