Observation of some new traps introduced by low-energy Ar + ion bombardment on n-GaAs

Abstract

Deep level transient spectroscopy (DLTS) measurements of metal-insulator-semiconductor (MIS) Schottky barrier diodes fabricated on low-energy Ar + ion bombarded (100) n-GaAs substrates are presented. The test devices consisted of liquid encapsulated Czochralski (LEC) substrates and of a double-layer structure prepared by growing a 2 μ m thick lightly doped MBE grown n-GaAs layer on n-GaAs substrates. The LEC samples show two DLTS emission peaks corresponding to trap levels 0.40 and 0.76 eV (EL2), below the conduction band edge, while the MBE grown samples were free of defects. The ion beam etched samples show two distinct electron traps, 0.32 and 0.52 eV below the conduction band edge, for both substrate categories. The DLTS spectra also indicate the appearance of a trap level at 0.69 eV. The evidence that these traps were found to be independent of the substrate material and the details of device processing conditions suggest that they were entirely ion beam etching (IBE) induced. For the ion beam etched LEC samples the DLTS emission peak at 0.40 eV stayed while the EL2 peak disappeared. The observed disappearance of EL2 peak was considered to be due to a defect complex formation, as proposed in our earlier report. Calculations indicate that defect densities at 0.32 and at 0.52 eV increase as a function of ion beam energy for both substrates. Calculations of the damage depth profile induced by IBE suggest that discrete trap centers form in a region deeper than predicted by the LSS range distribution theory.