ZnO based nanowires and thin films are widely utilized in piezotronics, piezo-phototronics and nanogenerators. The performance of piezotronics and piezo-phototronic strongly depends on the magnitude of piezopotential. By alloying Mg into ZnO, MgxZn1-xO of wider band gaps has been regarded as a good candidate for solar-blind UV sensors. In this study, high-performance self-powered ZnO-based photodetectors are developed by enhancing piezopotential through alloying with Mg. A series of n-MgxZn1-xO thin films (from x = 0 to 0.2) with strong c-axis preferred orientation in the wurtzite phase are grown on p-type Si substrate by magnetron co-sputtering. The Mg content is determined by energy dispersive spectroscopy (EDS) analysis in conjunction with photoluminescence (PL) where the results confirm the increasing trend on band gap with increasing Mg. The piezotronics and piezo-phototronics properties of photodetectors made of selective preferentially orientated MgxZn1-xO thin films are studied by investigating the coupling of electrical and optical characteristics on strain, which reveals different piezotronic phenomena with different Mg contents. The MgxZn1-xO thin films are of wurtzite structure with highly preferred 0002 orientation and the photodetectors exhibit unique characteristics of self-power, ultrafast response, and superior stability over time. The performance of the self-powered photodetectors enhances with Mg content due to the increase of the piezoelectric coefficient by the alloying process, and thus an enhanced piezopotential. An enhancement of up to 100% in the output current and voltage can be achieved through the piezo-phototronic effect. More notably, the sensitivity of the Mg0.20Zn0.80O self-powered photodetector is more than 6-fold higher than that of the Mg0.05Zn0.95O photodetector as a result of alloying with more Mg. The higher sensitivity with the higher Mg content in the MgZnO compound is attributed to the increased piezoelectric coefficient. The results demonstrate that the piezoelectric coefficient of MgxZn1-xO increases with Mg content, resulting in an enhancement of the effective piezopotential, which is responsible for the higher sensitivity of self-powered photodetectors. The developed material is thus a promising candidate for ultrahigh sensitive photodetectors.
National Cheng Kung University, Feng Chia University
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