Carrier concentration dependence of Ti ∕ Au specific contact resistanceon n -type amorphous indium zinc oxide thin films

Ti ( 200 Å ) ∕ Au ( 800 Å ) Ohmic contacts to n -type amorphous indium zinc oxide (IZO) films with carrier concentrations of ( 1 × 10 15 ) - ( 5 × 10 20 ) cm − 3 showed as-deposited specific contact resistances in the range of ( 3 × 10 − 1 ) - ( 1 × 10 − 4 ) Ω cm 2 . Postgrowth annealing from 200 to 500 ° C resulted in significant improvement in contact resistances due to increase of the carrier concentration in the near surface region of IZO layer, which can be attributed to the formation of Ti-O alloy phases that induce oxygen vacancies in the IZO. After annealing at 500 ° C , the lowest contact resistance of 8 × 10 − 6 Ω cm 2 was achieved in the sample with carrier concentration of 5 × 10 20 cm − 3 . Temperature dependent measurement showed that tunneling was dominant transport mechanism in the contacts on the most highly doped films ( n ∼ 5 × 10 20 cm − 3 ) and thermionic emission on the most lightly doped films ( n ∼ 1 × 10 15 cm − 3 ) .