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/sup +//sub 1/-i-p/sup +//sub 2/-n/sup +/ doping profile that enables electron collection in the Gamma -valley of GaAs is presented. In fabricated HBTs operating at low collector current density, f/sub 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/sub T/ value of 105 GHz obtained at a collector current density of 5*10/sup 4/ A/cm/sup 2/ also demonstrates the significance of the proposed near-ballistic collection structure. >