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 structur e may extend the optimum annealing temperature window down to 400 degr ees 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 regr own GaAs layer doped heavily with Ge formed. Special attention was pai d to confirm the mechanism of ohmic contact formation and a possible r eaction sequence was derived. After rapid thermal annealing at 600 deg rees 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 w as observed after sequential aging at 400 degrees C.