Patent ID: 6034382
Filing Date: 2000-03-07
Classification: H01L

Abstract:
A bipolar transistor, comprising:a substrate;a collector layer provided on said substrate, said collector layer having a first conductivity type;a base layer provided on said collector layer, said base layer having a second, opposite conductivity type;an emitter layer provided on said base layer, said emitter layer having said first conductivity type;an emitter contact layer provided on said emitter layer, said emitter contact layer having said first conductivity type; andan ohmic electrode provided on said emitter contact layer;said emitter contact layer including:a first layer of said first conductivity type, said first layer having a first bandgap;a second layer of said first conductivity type, said second layer being provided on said first layer and having a second bandgap larger than said first bandgap, said second layer having a sufficient thickness for allowing tunneling of carriers therethrough; anda third layer of said first conductivity type, said third layer being provided on said second layer and having a third bandgap smaller than said second bandgap.