Polar and non-polar growth of BeMgZnO quaternary alloy thin films for deep ultraviolet photodetectors

Abstract

This study demonstrates the successful growth of high-quality BeMgZnO epitaxial thin films with distinct crystallographic orientations (polar c-plane and nonpolar m-plane) for advanced deep-ultraviolet photodetection applications. Under 5 V bias, the developed Au/BeMgZnO/Au metal-semiconductor-metal photodetectors achieve ultra-low dark current (19.5 pA), high on/off ratio (3.11 × 10³), fast response speed (rise/recovery times: 2.81 s/0.22 s), and superior spectral selectivity (R₂₈₀/R₄₀₀ > 10³). The incorporation of Be and Mg effectively suppresses oxygen vacancy formation in ZnO lattices, reducing dark currents by six orders of magnitude (from mA to pA) compared to pure ZnO detectors while mitigating persistent photoconductivity. Comparative analysis reveals orientation-dependent dynamics: polar c-BeMgZnO detector exhibit faster recovery due to defect-assisted recombination at grain boundaries, enhancing photogenerated carrier annihilation. In contrast, non-polar m-BeMgZnO detector demonstrates significantly higher responsivity, attributed to the synergistic effect of intrinsic c-axis polarization field and applied electric field, which facilitates carrier separation and transport. Remarkably, the nonpolar m-plane configuration enables self-powered operation through polarization-induced built-in potential, achieving sensitive photoresponse under zero bias. These results establish crystallographic orientation control as a key determinant for optimizing detector performance, particularly in polarization-engineered energy-efficient UV photodetectors.