Transmission-electron microscope studies of Au-Ni-Ge based ohmic contacts to GaAs-AlGaAs MODFET device

A technique is developed to obtain cross-sectional transmission-electron microscope specimen of a specifically desired region of semiconducting devices. A Au-Ge-Ni based metallization scheme is used to obtain low resistivity ohmic contact to GaAs-AlGaAs based modulation-doped field-effect transistors device. Cross-sectional electron microscopy and energy dispersive x-ray analysis revealed that a uniformly alloyed region (Ni-Ge-As) can be obtained through the proposed metallization scheme. Transmission-electron diffraction, high-resolution electron microscopy, and optical-diffraction analyses are employed to determine the various phases in the contact region. Movement of contact materials both parallel and perpendicular to the device surface is observed at the metallization edges after alloying. Contacts stressed at elevated temperatures to the point of incipient instability are found to exhibit a rougher metal/semiconductor interface.