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

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 AgP2 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.