The effect of base-Schottky geometry on Si PBT device performance

Experimental device results are compared with two-dimensional numerical simulations of etched-groove Si permeable base transistors (PBT's). Both the simulations and experimental devices indicate that small variations in the metal-semiconductor contact area of the base fingers can lead to substantial (≥ 50-percent) deviations in key device parameters such as transconductance G
m
, threshold voltage V
T
, and intrinsic input capacitance C
in
. In spite of these variations, the maximum small-signal short-circuit unity-current-gain frequency f
T
does not change significantly because the maximum ratio of G
m
to C
in
remains nearly constant. In the experimental devices, f
T
is limited to about 40 percent of the predicted value due to parasitic capacitances (e.g., base pad capacitance).