Mechanism of Excellent Photoelectric Characteristics in Mixed-Phase ZnMgO Ultraviolet Photodetectors with Single Cutoff Wavelength

Mixed-phase ZnMgO (m-ZMO) thin films with a single absorption edge tuning from,similar to 3.9 to similar to 4.8 eV were realized on a-face sapphire (a-Al2O3) by plasma-assisted molecular beam epitaxy. The small lattice mismatch of both ZnO and MgO with a-Al2O3 should be responsible for the single and controllable absorption edge. Metal-semiconductor-metal (MSM) photodetectors were fabricated based on these m-ZMO films, and the devices have the single cutoff wavelength, which can be tuned from 335 to 275 nm. These devices possess low dark current (78 pA for m-Z(0.67)M(0.33)O, 11 pA for m-Z(0.59)M(0.41)O, and 4 pA for m-Z(0.39)M(0.61)O at 40 V) and high responsivity (434 A/W for m-Z(0.67)M(0.33)O, 89.8 A/W for m-Z(0.59)M(0.41)O and 3.7 A/W for m-Z(0.39)M(0.61)O at 40 V). Further response study reveals that the 90-10% decay time of m-Z(0.67)M(0.33)O, m-Z(0.59)M(0.41)O, and m-Z(0.39)M(0.61)O is around 37, 30, and 0.7 ms, respectively. Large amounts of heterojunction interfaces between wurtzite ZMO and cubic rock-salt ZMO could be responsible for the low dark current and high responsivity of our mixed-phase devices. The excellent comprehensive performance of m-ZMO UV photodetectors on a-Al2O3 suggests that m-ZMO UV photodetectors should have great applied potential.