KOH Wet Etching Ga-Polar AlGaN Epilayer for Ultraviolet B Photodetection With Low Dark Current and High Sensitivity

AlGaN ternary alloy is a potential candidate for visible blind or even solar blind photodetection application in extreme environmental conditions due to its excellent thermal stability and radiation hardness. However, the screw dislocations formed during the heteroepitaxial growth have proved to be responsible for high dark current, which is unfavorable to ultraviolet (UV) detection. In this study, KOH wet etching was adopted to eliminate the surface states of Ga-polar AlGaN epilayer and reconstruct the surface oxides. The dark current of the KOH-etched AlGaN epilayer was lowered by three orders of magnitude, leading to a high photo-to-dark current ratio (PDCR) of 870. X-ray photoelectron spectroscopy (XPS) indicated the upward surface band bending after etching and the increase of surface barrier height by 0.4 eV. UVB/UVA rejection ratio (
${R}_{{300}}/{R}_{{365}}{)}$
of the device was calculated to be 353, exhibiting the potential application in sensitive UVB photodetection. The study provides a facile way for enhanced UVB photodetection of AlGaN epilayer. The simple device structure, along with the easy manufacturing process, may facilitate the integration with other components on optoelectronic circuits.