Laplace DLTS study of defects introduced in GaAs during sputter deposition of Au Schottky contacts

The RF sputter deposition was used to fabricate Au Schottky barrier diodes on Si-doped n-type GaAs with two different carrier densities (1 × 1015 cm−3, 1 × 1016 cm−3 and partially 8 × 1016 cm−3) at a power of 150 W. Deep-level transient spectroscopy (DLTS) and Laplace DLTS were used to measure the electrical properties of the sputter-induced defects near the surface of the GaAs. By using DLTS, we found that the samples contained six defects (S1 (0.046 eV), S2 (0.22 eV), S3 (0.30 eV), S4 (0.55 eV), S5 (0.56 eV) and S6 of which three (S1, S3 and S5) were metastable and one (S4) was highly dopant concentration dependent. S6 was observed close to where the EL2 was expected, but had different properties and two components which could be resolved by Laplace DLTS: S6a (0.83 eV) and S6b (0.84 eV). The depth profile showed a difference in depth distribution of the defects in the samples which shows by increasing depth, a rapid decay of defect concentration. The electric field dependence of the S3 defect could be explained by a combination of Poole-Frenkel and phonon-assisted tunnelling mechanisms while for the S4 and S5 defects the emission of carriers indicate the phonon-assisted tunnelling. True capture cross-section measurements were done, and the S3 defect had a much lower capture cross-section than the S4 and S5 defects and the real capture cross-section of S3 and S4 defects is in the range of Auger mechanism while for the S5 defect indicates multiphonon emission. Finally, measurements as to the effect of annealing on I–V characteristics were carried out on the sputtered samples as well.