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

Abstract

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.

CVD-deposited Cu2O thin films with a record Hall hole mobility of 263 cm2 V−1 s−1 and field-effect mobility of 0.99 cm2 V−1 s−1

“…Interface traps can also capture holes, leading to a lower current and a lower implied mobility. The interface trap density ( D it ) at the semiconductor–dielectric interface can be estimated from the sub-threshold slope (SS) using eqn (3): 5,34 The extracted trap density is 2.6 × 10 12 , 6.7 × 10 12 , 2.4 × 10 13 , and 6.0 × 10 13 cm −2 eV −1 for Device 1, Device 2, Device 3, and Device 4, respectively. Overall, SiO 2 with the lowest defect state, the lowest surface energy, and the largest grain size has the lowest interface scattering.…”

“…Interface traps can also capture holes, leading to a lower current and a lower implied mobility. The interface trap density (D it ) at the semiconductor-dielectric interface can be estimated from the sub-threshold slope (SS) using eqn (3): 5,34…”

“…The record hole-mobility of 256 cm 2 V −1 s −1 was reported in 2009–2010 and has not been improved since then, despite repeated attempts, 1,20–22 In principle, such a high bulk mobility should yield remarkable p-channel TFTs, but that is not the case (Table 1). Only a few groups have successfully demonstrated p-channel Cu 2 O TFTs.…”

Enhancement of Photocatalytic Activity of Electrodeposited Cu2O by Reducing Oxygen Vacancy Density

“…The absorption edge was located at approximately 600 nm, corresponding to a band gap energy of 2.0 eV; this finding is in agreement with those of other methods, including electrochemical deposition, reactive sputtering, and thermal oxidation. 5,14,34,35 No significant difference in absorption at different Cu(CH 3 COO) 2 concentrations was observed at wavelengths of <600 nm. Figure 2b presents the Raman spectra of Cu 2 O at an excitation wavelength of 532 nm (2.1 mW μm −2 ), to which the vibrational modes of Cu 2 O were denoted.…”

“…The spectral response had an onset wavelength of 600 nm corresponding to the band gap energy of 2 eV. The spectral response was enhanced when the deposition time was increased from 5 to 35 S4). A higher cathodic current indicated a higher growth rate of Cu 2 O.…”