4H-SiC monolithic Darlington transistors with slight current gain drop at high collector current density

Abstract

Profit from high current gain features, 4H-SiC power Darlington transistor has the capacity for handling high current transmission. In this paper, monolithic Darlington transistors were fabricated using a simultaneous formation process for both n-type (emitter) and p-type (base) ohmic contact. The isolated device shows current gain of 1061 and 823 with collector current density ( J C) increasing from 200 to 800 A/cm2, exhibiting a slight current gain drop at high J C. By extracting the interface state density ( D it) between SiO2 and p-type 4H-SiC, it is found that this advantage owes to the improvement of the shallow bulk minority carrier lifetime in base region. Furthermore, ISE-TCAD (technology computer aided design) simulation was carried out to study the relationship between base minority lifetime and the current gain, from which the total base minority lifetime is estimated to be 48 ns. The open base breakdown voltage ( BV CEO) is 850 V at a leakage current of 2 μA due to the electric filed crowding at the isolation bottom between drive bipolar junction transistor (BJT) and output BJT. To solve this, non-isolated devices were also fabricated with improved BV CEO of 2370 V, indicating the superior potential of 4H-SiC monolithic Darlington transistors for high power application, while the current gain is deceased to 420, which needs further improvement.