CHARACTERISTICS OF PDIN OHMIC CONTACTS TO N-GAAS WITH A THIN GE LAYER

Effect of a thin (2 nm) Ge layer in PdIn ohmic contacts with different deposition structure were studied. An appropriate deposition structure may extend the optimum annealing temperature window down to 400 degrees C, whereas an inappropriate one lets the effect of a thin Ge layer be negligible. In the former case, specific contact resistances (rho(c)) were reduced significantly in low temperature range because a regrown GaAs layer doped heavily with Ge formed. Special attention was paid to confirm the mechanism of ohmic contact formation and a possible reaction sequence was derived. After rapid thermal annealing at 600 degrees C for 10 s, a rho(c) value of 2 x 10(-6) Omega-cm(2) was obtained. Also, a thin (4 nm) InxGa1-xAs layer with an average x value of 0.7 was observed in the metal/GaAs interface. Increment in rho(c) values was observed after sequential aging at 400 degrees C.