Electrical conductivity and effects of mechanical bending of flexible amorphous transparent conducting CdO-Ga2O3 films synthesized by room temperature sputtering

Abstract

Recently, amorphous ionic oxide semiconductors (AIOSs) have attracted much attention as materials for a wide range of next-generation flexible and transparent optoelectronic devices. Despite their amorphous nature, AIOSs are highly conducting due to their high mobility (>10 cm2/V-s) and electron concentration. Typically, they are grown at low temperature with large area uniformity, and hence are compatible with the fabrication of flexible and organic devices. In this study, we synthesize a new class of AIOS, CdO-Ga2O3 alloys on both glass and polyethylene terephthalate (PET) substrates by radio frequency magnetron sputtering at room temperature and explore their properties for flexible electronic applications. Our experimental results show that Cd1−xGaxO1+δ alloy films are amorphous with Ga content x>0.3 and within the amorphous composition range of 0.3<x<0.4 the films exhibit a high electron mobility of ~20 cm2/V-s and a low resistivity of ~2 × 10-3 Ω cm with a wide optical gap of ~3.4 eV. In order to determine if the Cd1−xGaxO1+δ alloy films are suitable for flexible electronic applications, the behaviors of their electrical resistivity after mechanical bending were also evaluated as a function of the bending radius Rb and number of bending cycles. We find that amorphous Cd1−xGaxO1+δ films are more resistant to repeated compressive (inner) bending than that of crystalline film. When Rb ≥ 10 mm, essentially no change in the electrical resistivity of the amorphous films is observed for compressive bending. On the other hand, crystalline films experience much less electrical degradation after tensile (outer) bending. SEM and AFM studies confirm that crystalline films with large grain size easily delaminate from the substrate under compressive bending, giving rise to severe electrical degradation. On the other hand, amorphous films degrade most likely through developing microcracks under repeated tensile bending. Our results suggest that amorphous Cd1−xGaxO1+δ alloy films with 0.3<x<0.4 have the desired electrical, optical and mechanical properties as transparent conductors for flexible optoelectronic devices.