OHMIC CONTACT TO N-TYPE BULK AND DELTA-DOPED AL0.3GA0.7AS/GAAS MODFET TYPE HETEROSTRUCTURES AND ITS APPLICATIONS

A Ni-Ge-Au based metal composition with a Pt layer, has been developed for the ohmic contact to n-type bulk and delta doped Al0.3Ga0.7As/GaAs MOdulation Doped Field Effect Transistor (MODFET) type heterostructures. This composition provides a smooth surface morphology, an edge definition better than 0.1-mu-m and reproducible electric properties after Rapid Thermal Annealing (RTA). Undoped cap layer MODFET heterostructures with spacer thickness varying from 5 nm to as high as 100 nm have been investigated. Ohmic contact behavior of bulk and delta-doped heterostructures with 5 nm spacer layers are compared. The contact resistances obtained for these structures range between 0.1 and 25-OMEGA mm at room temperature, and remain unchanged down to 4 K. The advantages of this contact will be illustrated in two applications.