Zn $_{1 - x}$ Mg $_{x}$ O Homojunction-Based Ultraviolet Photodetector

Zn_1-xMg_xO p-n photodiodes were fabricated on (0001) sapphire substrates using a pulsed laser deposition technique with different Mg contents. Ti-Au and Ni-Au metals deposited using vacuum evaporation were used as n-type and p-type contacts, respectively. The X-ray diffraction analysis showed the Zn_1-xMg_xO double layers have a single phase hexagonal wurtzite structure. The optical bandgap of Zn_1-xMg_xO films has been tuned from 3.27 to 4.26 eV by increasing the Mg content x=0.0 to x=0.34. Correspondingly, the cutoff wavelength of the resultant detectors varies from 380 to 284 nm. Zn_1-xMg_xO p-n photodiodes with different Mg contents exhibit very good performance, with a very low dark current (< 20 pA) at the bias voltage of 10 V. The ultraviolet to visible rejection ratio is more than three orders of magnitude.