Perpustakaan Digital ITB

Organic molecular monolayers (MoLs) havebeen used for improving the performance of various electronicdevice structures. In this work, the concept of organicmolecular surface modification is applied for improving theperformance of GaN-based metal?semiconductor?metal(MSM) ultraviolet (UV) photodetectors (PDs). Organicmolecules of phenol-functionalized metallated porphyrin(hydroxyl-phenyl-zinc-tetra-phenyl-porphyrin (Zn-TPPOH))were adsorbed on GaN, andNi/Zn-TPPOH/GaN/Zn-TPPOH/Ni PD structures were fabricated. This process wasbeneficial in two ways:first, the reverse-bias dark current was reduced by 1000 times, and second, the photocurrent wasenhanced by?100 times, in comparison to the dark and photocurrent values obtained for Ni/GaN/Ni MSM PDs, at highvoltages of±10 V. The responsivity of the devices was increased from 0.22 to 4.14 kA/W at 5?W/cm2optical power density at?10 V bias and at other voltages also. In addition to this, other PD parameters such as photo-to-dark current ratio and UV-to-visible rejection ratio were also enhanced. The spectral selectivity of the PDs was improved, which means that the molecularlymodified devices became more responsive to UV spectral region and less responsive to visible spectral region, in comparison tobare GaN-based devices. Photoluminescence measurements, power-dependent photocurrent characteristics, and time-resolvedphotocurrent measurements revealed that the MoL was passivating the defect-related states on GaN. In addition, Kelvin probeforce microscopy showed that the MoL was also playing with the surface charge (due to surface states) on GaN, leading toincreased Schottky barrier height in dark conditions. Resultant to both these phenomena, the reverse-bias dark current wasreduced for metal/MoL/GaN/MoL/metal PD structures. Further, the unusual photoconductive gain in the molecularlymodified devices has been attributed to Schottky barrier lowering for UV-illuminated conditions, leading to enhancedphotocurrent