Influence of the N2O Plasma Treated ZnO Seed Crystallites on Opto-Electrical Properties of Hydrothermally Grown ZnO Nanorods on Plastic Substrate

Abstract

ZnO nanorods (NRs) based flexible ultraviolet (UV) light detectors have promising applications for wearable and implantable health monitoring systems. However, their responsivity strongly depends on the crystalline quality of the NRs. Here, we propose N2O plasma treatment of the ZnO seed layer (SL) for the growth of high crystalline quality ZnO NRs on flexible polyethylene terephthalate (PET) substrates. In fact, the seed layer prepared at low temperatures, as required by flexible substrates, using sol-gel method contains acetates that result into small grain size of the seed crystallites. However, the N2O plasma treatment of the seed layer removes the acetates thereby providing better nucleation sites for subsequent growth of ZnO NRs due to an increased crystallites grain size. The full width at half maximum (FWHM) of (002) X-ray diffraction peak is decreased from 0.34 in the untreated seed layer based NRs to 0.29 in the plasma treated seed layer based NRs. Besides, improved near band edge emission (NBE) at 374 nm and aspect ratio of similar to 9.2 was demonstrated. UV detector based on the as-grown NRs showed similar to 4 times improvement in the on-off current ratio and similar to 30% decrease in the response and recovery times than the NRs grown on an untreated seed layer.