Passivation of InGaAs surfaces and InGaAs/InP heterojunction bipolar transistors by sulfur treatment

The surface properties of InGaAs(100) after ex situ treatment with (NH4)2S solution were investigated by photoluminescence (PL) and high-energy resolution x-ray photoelectron spectroscopy. The As 3d, Ga 2p3/2, and In 3d5/2 core level studies show that the surface is free of native oxides and is terminated by S after treatment. A dramatic increase (∼40 times) in the PL efficiency was observed on undoped InGaAs(100) surfaces after sulfur passivation. This S treatment has also been applied to the passivation of the extrinsic base of InGaAs/InP heterojunction bipolar transistors (HBTs). The effectiveness of the sulfur passivation treatment was confirmed by the resulting devices which exhibited dc current gain values of up to 200 at very low collector currents (nA). Further, the sulfur passivated HBTs do not show any dependence on the perimeter-to-area (P/A) ratio of the emitter junction which is of interest for high frequency characteristics while maintaining high current gain.