On the profile design and optimization of epitaxial Si- and SiGe-base bipolar technology for 77 K applications. I. Transistor DC design considerations

Silicon Germanium Heterojunction Bipolar Transistor for Digital Application

“…Our results show that SiGe HBTs with trapezoid Ge profiles have higher cutoff frequencies and higher maximum frequencies of oscillation, but lower current gain compared to SiGe HBT with flat Ge profiles ,which is consistent with previous research [20,21], which used trapezoid Ge profil for optimum SiGe HBT performance. The simulation results show that base width scaling, Ge profiles and Ge mole fraction have no significant effect to the ECL gate delay.…”

Influence of Fermi-Dirac Statistics on Collector Current of npn SiGe HBT at Low Temperatures

“…Since AEg,Ge,G is approximately linear function of Ge fraction, an effective trapezoidal Ge profile can be found for every grown trapezoidal Ge profile, doping concentration in the base and temperature (Fig.4b). Since the trapezoidal Ge profile can be treated analytically [2,4], the collector current in SiGe HBT with degenerately doped base and trapezoidal Ge profile can be modelled analytically by means of AE,,@ In this approach it is necessary to evaluate AE8,Ge,@ only at both edges of the base. The collector current then reads: The ratio of approximated collector current (eq.…”

“…As a consequence of bandgap narrowing in the base due to Ge and alloying, SiGe HBTs are well suited also for low-temperature operation [1,2]. It has been recently demonstrated that SiGe HBTs can achieve better performances at LNT (77K) than at RT (300K) [3].…”

“…Since the doping concentration in the base of SiGe HBTs operating at low temperatures should be high enough to prevent carrier freeze-out and to assure low base resistance, FD statistics instead of Boltzmann (B) statistics should be taken into consideration for analysis and optimization of low temperature base transport properties of SiGe HBTs. Existing analytical expressions for the collector current (Ic,,,,) and related properties of SiGe HBTs are generally based on B statistics [1, 2,4]. For this reason such expressions seem not to be appropriate for low-temperature analyses of SiGe HBTs [1,2].…”

“…Existing analytical expressions for the collector current (Ic,,,,) and related properties of SiGe HBTs are generally based on B statistics [1, 2,4]. For this reason such expressions seem not to be appropriate for low-temperature analyses of SiGe HBTs [1,2]. In this work we analyze the influence of FD statistics in the base of SiGe HBT, and propose a new approach to the analytical modelling of the collector current in SiGe HBT, taking FD statistics critically into account.…”