Passivation of graded-base InP/InGaAs/InP double heterostructure bipolar transistors by room-temperature deposited SiNx

Both the self- and nonself-aligned graded-base InP/InGaAs/InP double heterostructure bipolar transistors (DHBTs) were passivated by room-temperature deposited SiN_x. Current gains were found to increase after SiN_x passivation. The leakage current of base-collector junction was greatly increased by the passivation. The leakage current made the deformation of the common-emitter I-V curve in the nonself-aligned DHBT, while this did not occur in the self-aligned DHBT. The leakage current was caused by an accumulation layer between the SiN_x and InP. The leakage current could be decreased by the annealing at 300°C for 5 minutes.