Low resistance silver contacts to indium phosphide: Electrical and metallurgical considerations

Abstract

The electrical and metallurgical behavior of the Ag-InP contact system has been investigated. Specific contact resistivity (Rc) values in the low 10-6 Ω cm2 range are readily achieved on n-InP (Si: 1.7×1018 cm-3) after sintering at 400°C for several minutes. The low Rc values, however, are shown to be accompanied by dissolution of InP into the metallization, resulting in device degradation. An analysis of the sinter-induced metallurgical interactions indicates that this system is quite similar to the well-characterized Au-InP system, although there are some fundamental differences. The similarities include the dissociative diffusion of In, the reaction-suppressing effect of SiO2 capping, and, most importantly, the formation of a phosphide layer at the metal-InP interface. It is suggested that the low post-sinter Rc values in the Ag-InP system are due to the presence of a AgP 2 layer at the metal-InP interface. We show that it is possible to achieve low values of Rc without incurring device degrading metallurgical interactions by introducing a thin AgP2 layer between the InP and the current carrying metallization.