Influence of lattice misfit on heterojunction bipolar transistors with lattice-mismatched InGaAs bases

Abstract
AlGaAs/InGaAs/GaAs heterojunction bipolar transistors (HBTs) with lattice‐mismatched InGaAs bases have been studied for determining the effect of misfit defects on device performance. Defect structures were investigated using scanning cathodoluminescence and transmission electron microscopy. Misfit dislocations were found to form at the bottom interface between n‐InGaAs and n‐GaAs in the collector. Electrical properties of lattice‐misfitted n‐GaAs/n‐InGaAs heterojunctions were studied using p+‐GaAs/n‐GaAs/n‐InGaAs diode structures. Deep‐level transient spectroscopy measurements revealed electron traps (Et=0.49–0.55 eV) and hole traps associated with the lattice‐misfitted interface. Devices showed high dc current gains in spite of the presence of misfit dislocations. Poorer saturation of collector current was observed with increasing defect density. HBTS with lattice‐mismatched InGaAs bases are considered to be relatively insensitive to the introduction of misfit dislocations in terms of dc characteristics.