Conduction mechanisms of polysilicon emitters with thin interfacial oxide layers

Polysilicon emitter bipolar transistors containing a thin (∼30Å) oxide layer at the poly/mono-Si interface have been fabricated. Detailed electrical analysis of the devices shows, that the emitter base diode really is a n⁺-poly-Si/SiO2/p-mono-Si structure. The collector current is limited by combined thermal emission and tunneling mechanisms across an interface barrier in the conduction band of φB≈0.8V. The base current flows via tunneling and recombination at interface traps. The potential drop at the interface leads to a dramatic loss of transconductance in comparison to standard bipolar transistors. Application of this type of device for bipolar IC´s is therefore possible, if φBcan be significantly reduced by modification of the interface.