Lateral protrusions of ohmic contacts to AlGaAs/GaAs MODFET material

Cross-sectional transmission electron microscopy is used to determine the structure of Au-, Ge- and Ni-based ohmic contacts at the interface with AlGaAs/GaAs modulation-doped field-effect-transistor material. Significant lateral diffusion (?0.12?m) is found to occur at the edge of the contact during alloying. The observed contact structure places a limit on minimum geometries and must be taken into account if accurate device modelling is to be carried out.