EXCESS CAPACITANCE OF AL N-GAAS SCHOTTKY DIODES PREPARED ON AR-(AR+H)-ION-BEAM-ETCHED SURFACES/

The defects created during Ar-ion beam etching of Si-doped n-GaAs were envisaged by means of a charge version of deep-level transient spectr oscopy [DLTS - D.V. Lang, J. Appl. Phys. 45 (1974) 3023]. For ion beam energies from 200 to 700 eV there are two groups of radiation-induced gap states: a discrete energy level identified by its ionization enth alpy of 0.28 eV and a continuous distribution of surface traps in both energy and capture cross section. Excess time-domain capacitance coul d be observed under zero or reverse biases that is simply related to t he response of the defect states. Addition of a few % of hydrogen to t he Ar-ion beam manifested itself by lowering the charge-carrier densit y in the surface region of the heavily doped GaAs, while inducing a ca pacitance plateau in the C-U characteristics of Al/GaAs diodes at low temperatures. Despite only minor changes in the DLTS spectra in case o f moderately doped GaAs, the incorporation of hydrogen to GaAs led to observable hysteresis in the C-U behaviour. Finally, the nearly expone ntial response to a small voltage step of the continuum of surface sta tes is treated with emphasis on the expected high resistivity of the d amaged interlayer and an additional ultra-thin (8 nm) oxide layer.