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

Unlike most metal oxides, copper oxides (Cu2O and CuO) show p-type conductivity, which is required for many electronic applications. Cu2O has been reported to have relatively high hole mobility (256 cm2 V–1 s–1). Unfortunately, the thin-film deposition of pure Cu2O is not trivial. Pure-phase Cu2O is formed in a narrow pressure–temperature window, only under precise oxygen potential. To obtain pure-phase Cu2O, we have deposited Cu using chemical vapor deposition (CVD) and performed postdeposition oxidation without breaking the vacuum. As Cu2O is very sensitive to oxygen potential, the conditions for oxidation were derived from thermodynamic simulations to obtain pure-phase Cu2O. Hall measurement illustrates a significant Hall mobility of 80.9 cm2 V–1 s–1 for Cu2O. Films are intrinsically p-type doped with a carrier density of 2.3 × 1016 cm–3. To show its device application, thin-film transistors were fabricated on the Cu2O 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 cm2 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 Cu2O that can be used for electronic applications.