Microstructural and electrical investigations of Pd/Ge/Ti/Au ohmic contact to n-type GaAs

Interfacial microstructures of Pd/Ge/Ti/Au ohmic contact to n-type GaAs have been investigated using cross-sectional transmission electron microscopy? and the results are used to interpret the electrical properties. Annealing al 300 degrees C yields a contact resistance of 0.62 Omega mm and the layer structure is changed to GaAs/PdGe/Au4Ti/TiO. The ohmic contact is formed through a solid phase regrowth of GaAs heavily doped with Ce below the PdGe layer. At 380 degrees C, the lowest contact resistance of 0.33 Omega mm is obtained. The layer structure is changed to GaAs/(Ge-Ti)/PdGe/TiO. Spikes composed of Au and AuGa are found at the grain boundaries of the PdGe compound. The formation of AuGa at 380 degrees C reduces the contact resistance through the creation of more Ga vacancies al the interface of GaAs/PdGe, and the incorporation of elemental Ge. (C) 1996 American institute of Physics.