SiGe resonance phase transistor: active transistor operation beyond the transit frequency fT

Abstract For the first time it was possible to obtain a current gain increase to more than 0 dB at frequencies beyond the transit frequency f T by use of an SiGe resonance phase transistor (RPT). This was achieved by using a very thick base layer with a graded high content Ge profile and a thick low doped collector to get a large phase delay in the carrier drift and a delayed injection. Based on these ideas the so called RTP was fabricated. To get sufficient phase delay in the base, it is necessary to grow very thick base layers ( w B ) with graded Ge content ( x ) up to high Ge concentrations (i.e. w B =120 nm, x =5–30%). These structures were grown by MBE at low temperatures in the ultrametastable growth regime. The manufacturing of the transistors was performed by a low temperature process with temperatures below 450 °C, using a NiSi/Ag contact metallisation.