Regional Monte Carlo Modeling of Electron Transport and Transit-Time Estimation in Graded-Base HBT's   Xing Zhou, Member, IEEE  

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  Figures   Fig. 1 | Fig. 2 | Fig. 3 | Fig. 4 | Fig. 5 | Fig. 6 | Fig. 7 | Fig. 8 | Fig. 9 | Fig. 10 | Fig. 11 | Fig. 12     Fig. 1 Left axis: Threshold energy for intervalley scatterings between G and L/X valleys (solid lines) in Al_xGa_1-xAs as a function of Al composition. Scattering due to phonon emission (dashed lines) and absorption (broken lines) are also shown with composition-dependent phonon energies. Right axis: G-valley effective-mass ratio in Al_xGa_1-xAs (dotted line).       Fig. 2 Built-in field versus composition at various base widths using the quasi-linear relationship (2).       Fig. 3 Average velocity versus composition at various base widths.       Fig. 4 Average energy versus composition at various base widths.       Fig. 5 Valley population versus composition at various base widths.       Fig. 6 Average total scattering rate versus composition at various base widths.       Fig. 7 Transit time optimization curve: base width-composition combinations on which peak average velocities occur. Above this curve NDR and high-field effect are dominant; below this curve transport is in the low-field (Ohmic) regime; on this curve, optimum base transit times are expected.       Fig. 8 Base transit times versus composition at various base widths, using (7) (solid lines) and (8) (dotted lines).       Fig. 9 Average velocity versus built-in field for W = 1000Å and 1500Å. The field is mapped from composition using (2) (see Fig. 2).       Fig. 10 Base transit time versus base width at three constant fields (i.e., both W and x are varied but the slope of conduction band is kept constant).       Fig. 11 Average energy (---) and velocity (—) versus distance at a constant built-in field of 7 kV/cm. The end of each curve indicates the corresponding base width.       Fig. 12 Mobility versus composition at various base widths. The dots indicate where the peak velocities occur.