Effect of doping profile variations on the performance of the permeable base transistor

The cutoff frequency f
t
and maximum frequency of oscillation f
max
of the permeable-base transistor have been calculated for devices with a fixed geometry and different doping profiles to determine the profile that gave the highest value of
f_{\max}
The effect of different static velocity-field curves for GaAs and InP, and associated diffusion-field dependencies on device performance have also been examined. The results of the simulations show that the saturated velocity for GaAs PBT's has a major impact on performance. The uniformly doped device, N
d
of 4 × 10
¹⁶
cm
^-3
, has a higher
f_{\max}
when the saturated velocity is larger, but the effect of the low field mobility is small. The InP device has a slightly higher
f_{\max}
than the corresponding GaAs devices at this doping level. The 20-10-4 × 10
¹⁶
cm
^-3
devices have the highest
f_{\max}
of all the GaAs devices investigated.