A POSSIBLE NEAR-BALLISTIC COLLECTION IN AN ALGAAS GAAS HBT WITH A MODIFIED COLLECTOR STRUCTURE

An AlGaAs/GaAs heterojunction bipolar transistor (HBT) structure with an n-p** plus //1-i-p** plus //2-n** plus doping profile that enables electron collection in the GAMMA -valley of GaAs is presented. In fabricated HBTs operating at low collector current density, f//T reaches its peak value when the potential variation in the i collector layer is around 0. 4 V, which indicates that the electron transport is dominated by the GAMMA -valley feature in GaAs. A high f//T value of 105 GHz obtained at a collector current density of 5 multiplied by 10**4 A/cm**2 also demonstrates the significance of the proposed near-ballistic collection structure.