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

Abstract

Cuprous oxide (Cu₂O) is one of the few p-type semiconductor oxides that allow hole transport, making it useful for a variety of electronic applications, such as p-channel thin-film transistors (TFTs). Unfortunately, unlike n-type oxides, the performance of p-type oxide TFTs is poor. Even though Cu₂O has a reported bulk hole mobility of ∼250 cm² V⁻¹ s⁻¹, the best TFT mobility is 100-fold lower. In addition, the record performance has not been improved since 2009. This work shows a rational path to obtain a record hole mobility in Cu₂O films and devices. Using chemical vapor deposition, instead of the more commonly used physical vapor deposition method, precise control over the deposited film's nucleation rate and grain size is enabled. The grain size can be increased further by tuning the surface energy of the growth surface. These optimizations enable us to improve the bulk hole mobility from 53 to 263 cm² V⁻¹ s⁻¹, which is the highest mobility reported in Cu₂O thin films. We demonstrate p-channel thin-film transistors on four different dielectrics in the bottom-gate configuration, and we show that unpassivated bonds on the dielectric surface are the reason for the much smaller field effect mobility in Cu₂O thin films. The best TFT delivers a hole mobility of 0.99 cm² V⁻¹ s⁻¹, which is one of the highest values reported in the recent literature. More importantly, the results are repeatable and consistent in the mobility, subthreshold swing, and threshold voltage. Bias-stress studies show that the I–V characteristics show minimal drift, even after 1500 s of stress. The work is a significant advance for state-of-the-art p-type all-oxide electronics.