Spontaneous Generation of Carrier Electrons at the Interface between Polycrystalline ZnO and Amorphous InGaZnO₄

The interface between two materials can be expected to show exotic optical, electrical, and thermal transport properties due to the difference in chemical bonding and chemical potential. However, in conventional material systems, the volume fraction of the interface is small compared to bulk, and interfacial properties are thus difficult to utilize. In this regard, multilayered films are essential to increase the volume fraction of interfaces and functionalize their properties. Here it is shown that carrier electrons can be generated spontaneously at the interface between polycrystalline ZnO and amorphous (a-) InGaZnO₄. The electron transport properties are measured of multilayered films composed of c-axis oriented polycrystalline ZnO and a-InGaZnO₄ with varying interface density (d⁻¹). Although the carrier concentrations of both ZnO and a-InGaZnO₄ are less than 5 × 10¹⁹ cm⁻³, the n increases with d⁻¹ and exceedes 10²⁰ cm⁻³. The relatively large interface thermal resistance between ZnO and a-InGaZnO₄ (1.35 m² K GW⁻¹) indicates the existence of a large difference in the chemical bonding and the chemical potential and thus conduction electrons would accumulate at the interface.