Electrical characterization of Schottky contacts of Au, Al, Gd, and Pt on n-type and p-type GaAs

The Schottky barrier heights of several metals (Au,Al,Gd, and Pt) fabricated by electron-beam deposition on n- and p-type GaAs were measured with I-V, C-V,and photoresponse techniques. In the as-deposited state, all metals gave very similar I-V characteristics for n-type substrates with a barrier height qφ_b=0.63-0.65 eV and ideality factor n=1.20-1.45. The poor I-V characteristics in the as-deposited state were consistent with the higher barrier height determined with the C-V characteristics. Moderate annealing at 350°C for 30 min improved the I-V characteristics of all of them (qφ_b≅0.74 eV), as well as the photoyield in the internal photoemission process except the Au diode. No variation of the photothreshold energy was observed for n-type GaAs among the annealed contacts, suggesting that the Fermi-level is pinned by the native defects of GaAs. The barrier height was determined to be 0.90 eV for n-type GaAs. On p-type GaAs, the photothreshold energy varied and the barrier heights for Al,Gd,Au, and Pt were determined to be 0.89, 0.81, 0.70, and ohmic, respectively. The sum of the barrier heights for n and p type was therefore not equal to the band gap of GaAs. This implies that the pinning levels for n- and p-type surfaces are different. While there is pinning on a n-type surface, there is no pinning level for a p-type surface, so the barrier height on a p-type surface is dependent on the metal in contact.