The SIS tunnel emitter: A theory for emitters with thin interface layers

Silicon n-p-n transistors are made with emitters consisting of a polycrystalline and monocrystalline region with a thin (20-60-Å) "insulating" interfacial layer in between (SIS structure). These transistors show a remarkable increase in emitter efficiency with emitter Gummel numbers up to 7 × 10
¹⁴
s.cm
^-4
, and a low positive or even negative temperature coefficient of the current gain. A model is proposed to explain the mechanism in terms of tunneling through the interfacial layer. The electrical characteristics are measured in the temperature range 290-415 K. From the measurements it is deduced that the tunnel probability for holes (P
h
) is 10
^-2
to 10
^-3
and that for electrons (P
e
) is >10
^-5
. There also exists a band bending of 30-90 mV at the interfaces with the interfacial layer.