Improvement in Self-Powered GaN-based Symmetric Metal-Semiconductor-Metal Ultraviolet Photodetectors by Using Phenol-Functionalized Porphyrin Organic Molecules

Organic molecular monolayers have been used for improving the performance of various electronic device structures. In this work, the concept of organic molecular surface modification is applied for improving the performance and the self-power quality of GaN-based symmetric Metal-Semiconductor-Metal (MSM) Ultraviolet (UV) Photodetectors (PDs). Organic molecules of phenol-functionalized-metallated Porphyrin (Zn-TPPOH) have been adsorbed on GaN epitaxial layers and Ni/Zn-TPPOH/GaN/Zn-TPPOH/Ni PD structures have been fabricated. This process has led to decrease in reverse bias dark current by $\sim10,000 times$ at 0V in comparison to the dark current values obtained for Ni/GaN/Ni MSM PDs. Photodetector parameters such as Photo-to-dark current ratio and Responsivity have increased from 8.8 and 0.004 A/W for Ni/GaN/Ni structures to $2.4 \times10^{5}$ and 0.038 A/W for Ni/Zn-TPPOH/GaN/Zn-TPPOH/Ni structures, respectively at 0V. The spectral selectivity of the PDs has also improved at 0V, which means that the molecularly modified devices have become more responsive in UV spectral region and lesser in visible spectral region, if compared to bare-GaN based devices.