VACUUM ANNEALING CHARACTERISTICS OF ELECTRON-BEAM EVAPORATED RUTHENIUM CONTACTS TO N-GAAS GROWN BY ORGANOMETALLIC VAPOR-PHASE EPITAXY

High quality ruthenium Schottky barrier diodes were fabricated on organometallic vapour phase epitaxially grown n-GaAs, with a carrier density of 1 x 10(16) cm-3, by electron beam evaporation of ruthenium at a rate of 1 angstrom s-1. The annealing studies were carried out in vacuum over the temperature range from 225-degrees-C to 600-degrees-C. The electrical characteristics of the Schottky contacts were evaluated by standard current-voltage I-V and capacitance-voltage C- V measurements. The effective barrier height-phi(e)I-V and the flat band barrier height-phi(b)C-V of the as-deposited Ru-n-GaAs Schottky contacts were 0.865 eV and 0.916 eV respectively. These barrier heights reached their respective maximum values of 0.925 eV and 0.955 eV after annealing at 450-degrees-C. Auger electron spectroscopy results indicated that ruthenium forms structurally a very stable contact to GaAs, with no evidence of any chemical reactions between ruthenium and GaAs up to 500-degrees-C. Very limited diffusion of arsenic through the ruthenium layer was observed after annealing at 400-degrees-C. Diffusion of arsenic increased sharply after annealing at temperatures above 500-degrees-C.