Metal oxide semiconductor device technology is to date widely accepted as a technology that enable the development of next generation device applications such as flexible, transparent and low cost electronic devices because of its superior material properties such as reasonably high electron mobility (>10cm2(Vs)-1) and wide compatibility of processing including solution process. However, oxides with excellent electrical property are all n-type represented by a-In-Ga-Zn-O due to the unique electronic structures composed of a conduction band minimum (CBM) and valence band maximum (VBM) with different characteristics. The absence of high performance p-type oxide limits the device application and is largest drawback in oxide device technology. Therefore, next challenge is to develop high performance p-type oxide to realize p-channel TFT and complimentary circuit, and pn-juntion devices such as photovoltaic and light-emitting devices. To achieve this, it is imperative to develop not only a material exhibiting good hole transport but also to clarify impurity effect and in-gap defect structure and to develop an effective defect termination method.
Here I will present the development of high performance p-type oxide for TFT application and the complimentary inverter circuit composed of p/n-type oxides. Firstly, I will explain why the hole transport in oxide is so difficult and how we select p-type oxide candidates. Then I will show how to terminate in-gap defect for improving the device characteristics. Finally, I would like to discuss the material design for amorphous p-type oxide.