Extremely Low Contact Resistivity of Ti/Pt/Au Contacts on P⁺-Ingaas as Determined by a New Evaluation Method

A convenient method for determining a low contact resistivity p_c is described and experimental results are presented. Small dots of p⁺-InGaAson a thick and highly conductive substrate are metallized. The corresponding boundary problem of the current distribution is solved by using an integral equation which can be evaluated numerically. This method can be used to obtain p_c from experimental data. The procedure overcomes the difficulties usually encountered with the transmission line method since the inhomogeneity of the current density under the contact dots is fully taken into account. The exact knowledge of the diameter of the dots is imperative and must be examined using a scanning electron microscope. The p-Ino.53Gao.47As contact layer which is placed on a p-InP substrate (p = 6 • 10¹⁸ cm~³) is heavily p⁺-doped (2 • 10²° cm’³) using a zirconia-based diffusion source. Lowest p_c values obtained are smaller than 1-10“⁶ H cm², which are among the best for p-contacts ever reported.