Ultra-Low Resistance Ni-Based Contacts to n-InP: the Dependence of Contact Resistivity on the Condition of the Metal-Semiconductor Interface

Abstract

Near-theoretical-minimum values of specific contact resistivity, ρ_c (in the mid-to-low E-8 Ω-cm² range) have been achieved for Ni-based contacts to moderately doped (2E18 cm⁻³) n-type InP. In each case these values are an order of magnitude lower than those previously achieved. These ultra-low resistivities are shown to result when the metallurgical interaction rate between the contact metal and the semiconductor is sufficiently reduced. Several methods of reducing the metal-InP reaction rate and thus achieving lowered resistivity values are demonstrated. We show, for instance, that the introduction of a thin (100Å) Au layer at the metal-InP interface retards metal-semiconductor intermixing during sintering and results in a ten-fold reduction in ρ_c. Another method consists of ensuring the perfection of the near-surface InP lattice prior to and during contact deposition process. Use of this technique has enabled us to fabricate, for the first time, Ni-only contacts with ρ_c values in the low E-8 Ω-cm² range. We present an explanation for these observations that is based upon the magnitude of the In-to-P atomic ratio at the metal-InP interface.