Ion beam mixing for ohmic contact formation ton-Type GaAs

Electrical contacts have been formed on n-type GaAs (1.8 x 10¹⁸ carriers cm⁻³) using evaporated layers of 26 nm Ge/18 nm Ni or 40 nm Ge, with bombardment by 100-140 keV Se⁺ ions. After bombardment, the samples were annealed and the contact areas were subsequently coated, by evaporation, with Au for the Ge/Ni contacts or Ni + Au for the Ge contacts and then subjected to further thermal annealing. The objective is to induce ion beam mixing between Ni-Ge-GaAs or Ge-GaAs whilst simultaneously forming a heavily doped n-type region beneath the contact. The ion beam processing has been carried out for doses of 10¹⁴−10¹⁶ cm⁻² at temperatures ranging from 300-723K, followed by annealing at 693K for 120s for the Ge/Ni contacts and up to 1143K for the Ge contacts. In order to separate the doping effects from the ion beam mixing, bombardments were also undertaken using Kr⁺ ions. The specific contact resistance has been measured and the contacts further analysed using Auger depth profiling and RBS analysis. The contact morphology has been determined by SEM measurements.