Formation of extremely low resistance Ti/Pt/Au ohmic contacts to p-GaAs

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Abstract
Nonalloyed Ti/Pt/Au contacts to heavily doped p‐GaAs have been fabricated using effective cleaning of the semiconductor surface by bombardment with low energy Ar+ ions (60 eV) prior to the metal deposition. Short‐time annealing cycles for 1 and 20 s were employed in order to restore the primary properties of the subsurface layer disordered during ion bombardment. Annealing at temperatures ranging from 420 to 530 °C provides formation of contacts with an extremely low resistivity of 2.8×10−8 Ω cm2. A definite correlation between electrical properties and structural modifications of the contact interface was found. Measurements of the contact resistivity at different ambient temperatures yielded a good quantitative agreement with the theoretically predicted values using the field‐emission model. The results indicate that the metal‐semiconductor junctions formed under optimal conditions are intimate and that tunneling is the dominant mechanism of the current flow.