Preparation of transparent N-ZnO:Al / p-CuAlCrO 2 heterojunction diode by sol-gel technology

Abstract

This paper presents the study of oxide film heterojunction made of CuAlCrO 2 and ZnO:Al (AZO) deposited on fused quartz by sol-gel spin coating. Transmission electron microscopy (TEM) analysis has showed that the solvent, which was used to prepare the AZO sol, affects the thickness and planarity of the applied layers and the grain size of the polycrystalline film. The formation of a fine-grained structure of AZO films (grain size is up to 12 nm) leads to the formation of a smoother p-CuAlCrO 2 / n-AZO heterojunction. X-ray diffraction (XRD) analysis and TEM have revealed that the heterojunction was formed by AZO polycrystals, which orient axes [101] and [100] against the [101] and [006] directions in CuAlCrO 2 polycrystals. The optical transmission of the heterojunction in the visible range reached 70 %. The current –voltage (I-V) characteristics of p-CuAlCrO 2 / n-AZO corresponds to a diode one in the range from 4 up to 4 V. For the large values of the reverse bias, an increase in the leakage current is observed, which is associated with tunneling breakdown of heterojunction. The ideality factor of fabricated p-CuAlCrO 2 / n-AZO heterojunction is more than 2, which indicates the mechanisms of conductivity by defect-levels. In additional, it has been observed the response of the current-voltage characteristics to the green illumination (532 nm) of the diode that is associated with indirect band-gap absorption in CuAlCrO 2 . The impact of the white LED illumination had no effect on the current-voltage characteristics of the diode.