Lattice-strained heterojunction InGaAs/GaAs bipolar structures: recombination properties and device performance

Double‐heterojunction NpN GaAs/InxGa1−xAs/GaAs bipolar transistor layers have been grown by molecular‐beam epitaxy, and large‐area devices have been processed and characterized. The indium mole fraction in the strained base layer, and thus the band offsets, has been varied with significant differences in current gains. From the gain versus indium‐composition relation a valence‐band offset of ΔEv =9.7 meV/% In is derived. We found that the highest base‐In content yields the highest‐gain devices despite the presence of interface misfit dislocations and dark‐line defects.