The results of a comprehensive experimental and modelling investigation of high-frequency noise (HFN) of Si/SiGe:C and InP/InGaAs heterojunction bipolar transistors (HBTs) demonstrate that the key parameters to correctly model HFN for both HBTs are the self-heating (SH) effect at high collector injection levels, i.e. J C > 2-3 mA μm −2 , and the noise transport time (τ ) which must be included at all bias levels. In contrast, thermal noise contribution of the base-emitter junction of the Si/SiGe:C HBT, associated with the diffusive nature of electron transport at this junction because of the lack of conduction band discontinuity, is only important at operation frequencies lying in the frequency range f > f T /2. The noise analysis indicates that in order to correctly model HFN performances at any injection level and operation frequency, τ must be constant with bias and equal to the addition of base and collector transit times (τ B + τ C ). On the other hand, at high J C levels if SH is neglected, then the amplitude of the equivalent noise resistance (R n ) will be the most impacted noise parameter for both HBTs. Concerning the InP/InGaAs HBT, if SH is off at J C = 5.5 mA μm −2 , the minimum noise figure (NF min ) of the InP HBT will be underestimated by 10%.

We present an original and reliable technique to elucidate the different contributions to the apparent base resistance (R B = R Bx + XR Bi ) of double heterojunction bipolar transistors (HBTs) designed by Alcatel-Thales III-V Lab. The extrinsic base resistance (R Bx ) is quantified using small-signal measurements. The base-collector junction distribution factor (X) and the intrinsic base resistance (R Bi ) are extracted from high-frequency noise (HFN) measurements. This method was applied to three InP/InGaAs HBTs having different emitter surfaces (S E ). The correct determination of R Bx , X and R Bi may be a useful tool for compact and/or linear electrical modelling and may give some guidelines to designers to improve operation frequencies. Moreover, this strategy can be applied to any layout and technological variation of HBT; it can be also applied to homojunction bipolar transistors. Our results show that HFN analysis should be included to fully characterize bipolar transistors.