Non-alloyed ohmic contacts to n-GaAs using compositionally graded InxGa1−xAs layers

Non-alloyed ohmic contacts to n-GaAs using compositionally graded InxGa1-xAs layers grown by molecular beam epitaxy are studied. The carrier concentration reduction in the GaAs buffer layer due to low growth temperature is found to increase overall contact resistance for an n+-InAs/InxGa1-xAs(x=1→0)/GaAs structure. The lowest specific contact resistance (ρc) ever reported, 5×10-9 Ω cm2, is obtained with a 2×1019 cm-3 Si-doped structure grown at 450°C. A similar ρc value is also obtained when the InAs mole fraction is higher than 0.7. Using WSi as a contact metal, a refractory ohmic contact is realized in which ρc remains less than 2×10-7 Ω cm2 under annealing up to 800°C.