Giant UV Photoresponse of GaN-Based Photodetectors by Surface Modification Using Phenol-Functionalized Porphyrin Organic Molecules

Abstract

Organic molecular monolayers (MoLs) 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 of GaN-based metal–semiconductor–metal (MSM) ultraviolet (UV) photodetectors (PDs). Organic molecules of phenol-functionalized metallated porphyrin (hydroxyl-phenyl-zinc-tetra-phenyl-porphyrin (Zn-TPPOH)) were adsorbed on GaN, and Ni/Zn-TPPOH/GaN/Zn-TPPOH/Ni PD structures were fabricated. This process was beneficial in two ways: first, the reverse-bias dark current was reduced by 1000 times, and second, the photocurrent was enhanced by ∼100 times, in comparison to the dark and photocurrent values obtained for Ni/GaN/Ni MSM PDs, at high voltages of ±10 V. The responsivity of the devices was increased from 0.22 to 4.14 kA/W at 5 μW/cm2 optical 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 molecularly modified devices became more responsive to UV spectral region and less responsive to visible spectral region, in comparison to bare GaN-based devices. Photoluminescence measurements, power-dependent photocurrent characteristics, and time-resolved photocurrent measurements revealed that the MoL was passivating the defect-related states on GaN. In addition, Kelvin probe force microscopy showed that the MoL was also playing with the surface charge (due to surface states) on GaN, leading to increased Schottky barrier height in dark conditions. Resultant to both these phenomena, the reverse-bias dark current was reduced for metal/MoL/GaN/MoL/metal PD structures. Further, the unusual photoconductive gain in the molecularly modified devices has been attributed to Schottky barrier lowering for UV-illuminated conditions, leading to enhanced photocurrent.

Recent Progress of Heterojunction Ultraviolet Photodetectors: Materials, Integrations, and Applications

“…The hybrid PDs based on p‐type organic molecules with tunable functionality and n‐type inorganic semiconductors with superior intrinsic carrier mobility, usually present high photodetecting performance, thanks to the efficient separation and transfer of photoinduced charge carriers resulting from the p‐n heterojunctions. Various kinds of organic materials, such as polyaniline (PANI),90 poly(vinyl alcohol) (PVA),91 poly(arcylonitrile) (PAN),27 poly(vinyl carbazole) (PVK),92 polypyrrole (PPy),93 and even pyrene‐tricyanofuran derivatives,94,95 are also adopted to modify the photoelectric properties of semiconductor‐based PDs 96…”

Photovoltaic and flexible deep ultraviolet wavelength detector based on novel β-Ga2O3/muscovite heteroepitaxy

“…The photocurrent rise and decay curves can be fitted with biexponential Eq. 2 and 3 , respectively: 14 , 23 , 40 where I s represents the steady-state current and A and B are the fitting constants. τ r1 and τ r2 are fast and slow components of rise times whereas τ d1 and τ d2 denote the fast and slow components of decay times.…”

“…Nowadays, Ga 2 O 3 and AlGaN are the most widely used wide bandgap semiconductors for deep UV photodetector applications 14,[34][35][36][37][38][39][40][41] . Recently, Ga 2 O 3 has emerged as a better candidate than AlGaN due to its intrinsic deep UV absorption which eliminates the complexity of heavy doping 42 .…”

Recent developments in flexible photodetectors based on metal halide perovskite

“…In addition to organic semiconductor materials, other organic materials such as Rhodamine, phthalocyanine dyes, porphyrin, chlorophyll etc. also have been applied in PDs . For example, Xie et al designed a planar flexible photodetector with a bulk‐heterojunction architecture by spinning MAPbI 3 and Rhodamine B (RhB) precursor solutions on plastic substrate with interdigitated Au electrodes .…”