Backside secondary ion mass spectrometry study of a Ge/Pd ohmic contact to InP

Abstract

High-resolution SIMS (secondary ion mass spectrometry) depth profiles of Ge/Pd ohmic contacts on InP are obtained by sputter-etching from the back (semiconductor) side. The samples contain an InGaAs-etch stop layer, to allow chemical thinning, and InGaAsP marker layers, which allow alignment and calibration of the depth profiles on the nm scale. At 200 °C, a Pd-In-P alloy layer is observed to form at the contact interface. The thickness of this layer is dependent on the amount of metallic Pd available for reaction. Subsequent processing at 325 °C results in the partial dissolution of this alloy layer, as PdGe forms at the contact interface, and regrowth of the liberated InP. Ge is detected in the regrown region but is not observed to diffuse into the substrate. Ge epitaxy is not observed at the contact interface at 325 °C, in contrast to the behavior of the Ge/Pd-GaAs contact. The experimental evidence suggests that regrowth is a key step in the formation of the ohmic contact.