GaAs/Ta2O5 and GaAs/Al2O3 interface structures

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Abstract
Tantalum and aluminum oxides were grown on n-type GaAs by thermal oxidation of Ta and by anodic oxidation of vacuum deposited Ta and Al films. The insulating properties of these films are better than those of the native oxide films on GaAs. The interface properties of the GaAs/Al2O3 interface are better than those of GaAs/Ta2O5 structures obtained so far; this is due to the fact that the interaction between GaAs and Al and/or Al2O3 is less than that occurring during oxidation of Ta on GaAs. Even a relatively small film–substrate interaction can deteriorate the properties of the oxide film and the interface. However, some controlled interaction is desired to obtain good interface properties but it is difficult to achieve. Preliminary C–V measurements at 1 MHz indicate that the properties of the GaAs/Al2O3 interface depend on the original GaAs/Al interface. If a thin native oxide is present, then the accumulation capacitance is lower than the insulator capacitance; this effect is probably due to accumulation of arsenic at the interface. From the capatitance minimum it was also found that the effective donor density at the GaAs surface decreased by about one order of magnitude; this is probably due to Ga migration during the oxidation. However, an important observation was that an accumulation capacitance coinciding with the insulator capacitance could be obtained if a preoxidation heat treatment of the GaAs/Al interface was employed. This allows the incroporation of the room ambient oxide film on GaAs into Al2O3 film; i.e., a new interface is established which has promising properties, but the essential features of the Al2O3 films are maintained.

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