Two-Step Process using MOCVD and Thermal Oxidation to Obtain Pure-Phase Cu₂O Thin Films Transistors

Unlike most metal oxides, copper oxides (Cu 2 O and CuO) show p-type conductivity, which is required for many electronic applications. Cu 2 O has been reported to have relatively high hole mobility (256 cm 2 V –1 s –1 ). Unfortunately, the thin-film deposition of pure Cu 2 O is not trivial. Pure-phase Cu 2 O is formed in a narrow pressure–temperature window, only under precise oxygen potential. To obtain pure-phase Cu 2 O, we have deposited Cu using chemical vapor deposition (CVD) and performed postdeposition oxidation without breaking the vacuum. As Cu 2 O is very sensitive to oxygen potential, the conditions for oxidation were derived from thermodynamic simulations to obtain pure-phase Cu 2 O. Hall measurement illustrates a significant Hall mobility of 80.9 cm 2 V –1 s –1 for Cu 2 O. Films are intrinsically p-type doped with a carrier density of 2.3 × 10 16 cm –3 . To show its device application, thin-film transistors were fabricated on the Cu 2 O and CuO films, showing typical p-channel accumulation mode transistor characteristics with field-effect mobilities of 4.3 × 10 –2 and 2.4 × 10 –3 cm 2 V –1 s –1, respectively. Overall, material and electrical characterization show that metal-organic CVD along with oxidation is a promising option to achieve pure-phase Cu 2 O that can be used for electronic applications.