Controlling the p-Type Conductivity and Composition Range for Bipolar Conduction in NixCd1-xO Alloys by Acceptor Doping

Oxide-based transparent p-n homojunctions are desirable for the development of transparent electronics. However, most oxide semiconductors are intrinsically n-type and to achieve p-type wide-gap oxide is still challenging. Previously, we have demonstrated that alloying a high-mobility n-type material such as CdO with p-type NiO can provide an avenue for electronic band engineering and consequently achieve bipolar conductivity in the midalloy composition. In this study, we synthesized O-rich NixCd1-xO alloys (NixCd1-xO1+delta) over the entire composition with Li and Cu doping using radio frequency (RF) magnetron sputtering at room temperature. We show that by Li and Cu doping the conductivity in the p-type regime of these alloys is improved, which also leads to a wider composition window for bipolar doping in NixCd1-xO. Specifically, by Li doping, the p-type alloy composition can be extended to x >= 0.3 so that the bipolar doping window is expanded to 0.30 <= x <= 0.52. Detailed measurements on electrical, structural, optical, and electronic properties suggest that Li is an effective acceptor, offering a promising way to improve the p-type conduction in Ni-rich NixCd1-xO alloys as well as to regulate the bipolar conductivity in this alloy system. A p-Ni0.7Cd0.3O:Li/n-Ni0.45Cd0.55O quasi-homojunction was fabricated and a rectification ratio similar to 10(2) with an ideality factor of similar to 2.9 was obtained. The demonstrated quasi-homojunction structure also showed >60% transmittance in the visible spectrum.