Abstract
A new version of simple GaAs n + -n-δ(p + )-n- n + ultrathin base transistor with U-groove base contact is demonstrated by molecular beam epitaxy which possesses a circular mesa etched base. The potential barrier height can be directly modulated by the applied base voltage and thus the current can traverse over the barrier by thermionic emission. It is a voltage-controlled device. Its transconductance increases with increasing collector-emitter and base-emitter voltage. The collector current density of the present device is larger than 1.5 kA/cm 2 and the transconductance is larger than 200 mS/mm, which are larger than those of the previously reported V-groove device.