In/GaAs reaction: Effect of an intervening oxide layer

The effects of a thin (∼1.3 nm) intervening native GaAs oxide interface layer on the In/GaAs reaction have been investigated by comparing the reactions of In on GaAs substrates with the native oxide present or desorbed. Transmission electron microscopy of cross-sectional samples reveals that the thin native oxide layer, when present, disrupts the In/GaAs orientation relationship in as-deposited samples and prevents an extensive reaction between In and GaAs at 350 °C. These data also show that the In/GaAs reaction at 350 °C proceeds by dissolution of the GaAs substrate into the molten In followed by the subsequent nucleation and growth of epitaxial In1−xGaxAs particles with x≤0.2 or x≥0.8 only, indicating immiscibility. The In1−xGaxAs/GaAs interfaces are found to be structurally and compositionally abrupt to within ∼3 nm. The effects of the interfacial native oxide on the In/GaAs reaction and the suggested presence of an InAs-GaAs miscibility gap have implications for the fabrication of In/GaAs ohmic contacts by thermal reaction.