Molecular‐beam epitaxial growth of heavily acceptor doped GaAs layers for GaAlAs/GaAs heterojunction bipolar transistors

Heterojunction bipolar transistor (HBT) structures with heavily carbon and beryllium doped base layers were grown in a conventional molecular‐beam epitaxy (MBE) environment. The current gain in the carbon doped structures was reduced by enhanced bulk recombination. For a hole concentration of 5 × 1019 cm−3, the carbon concentration exceeded the hole concentration and is a likely cause of the enhanced recombination. Growth conditions were determined which minimized beryllium diffusion for HBT structures with base layers doped to 1.2 × 1020 cm−3. Lattice contractions were observed at high beryllium doping concentrations. The expected reduction in resistivity with increased beryllium base doping was obtained in the HBT structures. Using HBT structures doped with beryllium at 5 × 1019 cm−3, high‐power performance was obtained at 10 GHz.