The electrical behavior at room temperature of a Si BJT, a Si HBT with SiGe
narrow-bandgap base, and a GaAs HBT with AlGaAs wide-bandgap emitter was studied in a
comparative way using the same geometry and HBT typical doping profiles
with high base doping concentration of cm. The possibility to
perform such simulations was presented in [195].

Later on in [124] a material composition optimization was shown. The
optimization is automatically run using the VISTA framework [196] with
ten operating points distributed at equal distances of 11 nm over the 100 nm
thick SiGe base starting from constant 20% Ge content constrained to 25%. The
possibility to increase the maximum current gain and cutoff frequency by
material optimization can be seen in Fig. 4.2 and Fig. 4.3.

The cutoff frequency
is determined using the quasi-static approximation,
which can give results close to those from a small-signal analysis, as shown in
[158]

(4.1) | |||

(4.2) | |||

(4.3) |

Thus, by applying small steps of , can be calculated by

(4.4) |

where is the change of the total charge in the device.

Furthermore, the impact of new mobility and bandgap narrowing models of

2001-02-28