Fabrication of flexible UV-B photodetectors made of Mg_xZn_1-xO films on PI substrate for enhanced sensitivity by piezophototronic effect

In spite of intense research in MgZnO films for photodetector application, growth of MgZnO over a flexible substrate especially utilizing piezophototronic effect could hold a more promising approach. We demonstrate high performance UV-B photodetectors fabricated by using high quality, single phase, wurtzite Mg_xZn_1-xO thin films deposited on a polyimide substrate by magnetron sputtering. The Mg content in the Mg_xZn_1-xO films varies from 38.5 at.% to 44 at.% by changing the substrate temperature from room temperature to 250 °C. The MgZnO films have columnar nanorod like morphology and are highly oriented along the c-axis. The metal-semiconductor-metal photodetectors of the MgZnO films have achieved significantly high light to dark current ratio (~1630). The peak responsivity is 0.3 mA/W at 292 nm with a cutoff wavelength of 305 nm at 9 V bias voltage, selectively detecting the UV-B region (280 nm-320 nm) of electromagnetic spectrum and the UV-B-visible rejection ratio (~2.34×10⁵) is much higher than MgZnO PDs on rigid substrates. The performance of the Mg_xZn_1-xO photodetector is further enhanced under applied strain leading to significantly higher photocurrent (~4 µA) and light to dark contrast ratio (~11000), resulting in large boost in the sensitivity to light by 20 % depending on Mg concentration. The sensitivity to light (~20%) at a fixed strain of +0.29 % or -0.29% is also four times higher as that with 0 strain (~5%) demonstrating the synergistic effect of the piezophototronic effect along with the flexible substrate over the performance of the PDs.