Investigation of the mechanism of transport across the poly/monocrystalline silicon interface in polysilicon-emitter bipolar transistors based on variations in the interface treatment process

Electrical transport across the poly/monocrystalline silicon (poly-Si/c-Si) interface has been investigated byintroducing variations in the interface treatment process affecting the thickness of the native oxide layer formed on thesilicon surface. The I-V relationship characterizing the resistance associated with this interface is extracted using animproved open-collector method, which eliminates the inherent nonlinearity arising from the reverse active characteristicsof the bipolar transistor. The nonohmic behavior of the interface at low electric fields is demonstrated to be consistentwith direct tunneling through a rectangular barrier presented by an ultrathin interfacial oxide layer. An approximatetunnel junction model is proposed that fits the tunneling current in the low bias regime, predicting the experimentallyobserved increase in the low-voltage leakage current associated with ultrathin oxides. The thickness of the interfacialoxide extracted by fitting the measured data to the proposed rectangular-barrier tunnel junction model is in goodagreement with reported experimental values. Finally, a relation between experimentally introduced variations in theinterface treatment process and the magnitude of the resistance associated with the interface is identified, which can bequantitatively explained based on the direct tunnel junction model in terms of differences in the native oxide thickness.

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