High mobility p-type thin film transistors based on Cu2O semiconducting channels deposited from solutions at low temperatures

Rapid advances in the development of electron transporting oxide semiconductors have stimulated the rapid advancement of high charge carrier mobility devices making them ideal candidates for large-area electronics and optoelectronics. However, the lack of hole-transporting oxides of comparable performance has limited the realisation of the ubiquitous CMOS circuit architecture using such materials. Although there has been sporadic reporting on p-type character by doping of traditional n-type oxides, the subject still remains controversial so alternative metal oxides that show intrinsic p-type characteristics are still required. Here, we report on the deposition and characterisation of Cu2O films grown by spray coating at temperatures in the range between 150 ºC and 400 ºC from alkaline solutions of Cu2O. The films were investigated by means of UV–Vis spectroscopy, x-ray diffraction, AFM, and field-effect measurements. Analyses of Cu2O reveal deposition of cubic Cu2O films at deposition temperatures of about 250 ºC. Further increase of the substrate temperatures in excess of 270 oC yields films that are dominated by the CuO phase accompanied by deterioration in the electronic transport properties. TFTs employing Cu2O semiconducting channels deposited at optimal conditions (in terms of the solution’s pH and deposition temperature) on Y2O3 dielectrics, show excellent carrier transport characteristics such as low off currents, hole mobility of about 4 cm² /Vs and on/off current modulation ratio on the order of 104