Surface Modification of AlN Using Organic Molecular Layer for Improved Deep UV Photodetector Performance

A direct wide bandgap of 6.2 eV, high temperature robustness, and radiation hardness make aluminum nitride (AlN) a preferable semiconductor for deep ultraviolet (UV) photodetection. However, the performance and reliability of AlN-based devices is adversely affected by a large density of surface states present in AlN. In this work, we have investigated the potential of a monolayer of organic molecules in passivating the surface states of AlN, which improved the performance of AlN-based metal–semiconductor–metal (MSM) deep UV photodetector. The organic molecules of the meso-5,10,15-triphenyl-20-(p-hydroxyphenyl)porphyrin Zn(II) complex (ZnTPP(OH)) were successfully adsorbed on an AlN surface, forming a self-assembled monolayer (SAM). The molecular layer was characterized by contact angle measurement, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The surface modification of AlN effectively reduced the dark current of the photodetector by 10 times without degrading the magnitude of photocurrent, especially at low voltages. The photo to dark current ratio (PDCR) was enhanced from 930 to 7835 at −2 V, and the responsivity doubled from 0.3 to 0.6 mA/W at 5 V. Moreover, the rise and fall times of the detector were found to decrease after the surface modification process. Our results suggest that SAM of porphyrin molecules effectively passivated the surface states in AlN, which resulted in improved photodetector performance.