Improved design of the gallium arsenide permeable base transistor

Predictions of improved high-frequency performance of the gallium arsenide permeable base transistor (PBT) have been made by the exact diffusion-drift two-dimensional numerical analysis of several PBT designs. In this study both the device geometry and/or the impurity doping profile were varied and the corresponding unity-current-gain frequency f
T
calculated. More than a 35-percent improvement in f
T
was predicted when the ratio of the metal (Schottky) gate width to the space between gate fingers was varied. More than a doubling of f
T
could be obtained when the source and drain doping was increased to produce an n
⁺
-n-n
⁺
configuration. A UPBT structure was investigated where the semiconductor material above the gate electrode was removed in order to reduce this region's contribution to the capacitance. A 100-percent improvement in high-frequency performance was predicted for this structure, operating at low gate voltages due to improved g
m
as well. Less gain was obtained at higher voltages. Control of the surface states on the exposed "walls" of this device must be provided to obtain this advantage.