Npn abrupt AlGaAs/GaAs heterojunction bipolar transistors with thin base widths (WB) down to 200Å have been fabricated for the first time, and their collector and base current-voltage characteristics have been studied. The experimental results show that the surface recombination base current and the base bulk recombination current are both significantly lower in 200Å base HBTs than in comparable devices with 500Å base width. For the thin base HBTS, the base bulk recombination current density is proportional to ~∼WB and the surface recombination current density is proportional to ∼WB2. The experiment also showed that the collector current across a thin p+ GaAs base is limited, as expected, by the thermal velocity of the electrons rather than by conventional diffusive transport.
- Aluminium gallium arsenide
- Gallium arsenide
- Heterojunction bipolar transistors