FORMATION OF EXTREMELY LOW-RESISTANCE TI/PT/AU OHMIC CONTACTS TO P-GAAS

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-degrees-C provides formation of contacts with an extremely low resistivity of 2.8 X 10(-8) OMEGA 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.