The influence of interfacial morphology and composition on the behaviour of AuGeNi contacts to InP

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Abstract
A correlation between electron microscopy, secondary-ion mass spectroscopy (SIMS) and electrical measurements is reported for AuGeNi alloyed contacts to InP. Changes in the morphology and in the composition of the material at the interface show strong trends as a function of the initial alloy temperature and of subsequent heat treatment to simulate accelerated device operation. Dramatic changes in the electrical properties of the contacts are shown to follow closely and consistently the changes in morphology. The principal factor controlling the stability of the contact appears to be the thickness and integrity of a new AuGeP phase at the interface. Growth of large particles of Au2P3 occurs at high alloy temperatures or after prolonged heat treatment and is strongly associated with contact degradation. There was no evidence for preferential Ge diffusion. Various models for current transport across the metal-semiconductor interface are discussed as well as the implications for the control of contact resistance.