Influence of Ru3+ ions at Al2O3/GaAs interface on MIS structures

In addition to better electronic properties than silicon, gallium arsenide exhibits interesting optical properties. It is possible to realize the integration of both electronic and optical functions on the same GaAs wafer. However, its interfacial properties limit the use of GaAs for electronic devices (MIS, MESFET, etc.) [Electron. Technol. 27 (2) (1994) 69; J. Electron. Mater. 31 (1) (2002) 71]. Heller [U.S. Patent 4 (1981) 213] has proposed chemical treatments of GaAs surface by selenide and ruthenium solutions that induce an increase in electrochemical photocell yield. Two alternative explanations have been proposed to account for this effect: the first is by Heller [Acc. Chem. Res. 14 (1981) 154] who has assumed a decrease in surface states density and the second is by Aspnes [Surf. Sci. 132 (1983) 406] who has assumed a shift in surface Fermi level. Our result, using MIS structures as test (on untreated and treated surfaces) of interface quality is in a good agreement with Aspnes' proposal. We have found in fact that Heller's treatment shifts surface Fermi level to valence band and increases the surface state density. We assume that a generation recombination process that can probably be produced in the space charge region accounts for the observed kinetics of these states, which behave as hole traps. The fraction of a monolayer of ruthenium has been evidenced by means of radioactive tracer technique. We have concluded that these treatments do not improve MIS behavior. The main interest of this treatment remains the enhancement of electronic transfer kinetics at GaAs electrolyte solution interface.