Investigation on the effect of annealing process parameters on AuGeNi ohmic contact to n-GaAs using microstructural characteristics

The electrical and structural properties of AuGeNi ohmic contact to n-GaAs have been studied. A combination of EDX and X-ray diffraction analysis was used to examine the reactions between AuGeNi-based metallization and GaAs. Scanning Tunneling Microscope (STM) was used to study surface morphology and surface roughness. By the use of Rapid Thermal Annealing (RTA), contact resistivity as low as 5.5 × 10−8 Ω cm2 have been obtained. The minimum in the contact resistivity coincides with the formation of AuGa and NiAs phases. On the other hand, poor thermal stability after contact formation was concluded to be due to the formation of low melting point AuGa phases. Formation of dark particles, recognized as GeNi particles, in different distributions and shapes after annealing, was found to be essential for low contact resistivity. Correlation between GeNi particles distribution and contact resistivity was found and introduced as d/λ parameter. It was found that the lower the size of these particles (d) as well as the larger the contact area over which they are distributed (λ) leading to the better contact resistivity.

► Relationship between annealing parameters and contact resistance were found.
► Dark particles, GeNi, were found to be essential for low contact resistance.
► A new parameter in the form of d/λ was introduced.
► Optimum conditions for annealed AuGeNi/GaAs were reported.
► Formation of different phases during annealing was investigated.