A Study 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 metallizations and GaAs. Scanning Tunneling Microscope (STM) was used to study surface morphology and surface roughness. By the use of Rapid Thermal Annealing (RTA), contact resistances as low as 5.5×10^-8 Ωcm have been obtained. The minimum in the contact resistance 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 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 resistance. Correlation between GeNi particle 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 resistance.