The current-voltage (I-V) and capacitance-voltage (C-V) characteristics of Al/n-GaAs and Al/p-GaAs diodes on GaAs substiate treated by Ru3+ Ions are investigated and compared with characteristics of GaAs diodes on GaAs untreated Substrates The diodes does not have to show ail ideal behaviour of I-V characteristic with an ideality factor of 1.13 and barrier height of 0.85 eV and 0.6 eV for Al/n-GaAs and Al/p-GaAs diodes respectively The forward bias saturation current found with a big value (10(-10) A, 10(-12) A) in the Al/n-GaAs (untreated) Schottky diodes compared with Al/n-GaAs (treated) diodes Contrary the forward bias saturation Current found with a small value (10(-7) A. 10(-6) A) in the Al/p-GaAs (untreated) Schottky diodes compared with Al/p-GaAs (treated) diodes The energy distribution of interface states was determined from the forward bias I (V) characteristics. The interface states density found large in the Al/GaAs (treated by Ru3+ ions) structure comparing with the Al/GaAs (untreated) structure In parallel with electrical measurement, the Ru3+ adsorption on treated GaAs surfaces was controlled by photoelectrochemical and electrochemical measurements and by Auger analysis (c) 2009 Elsevier B.V. All rights reserved