Tunable Band‐Selective UV‐Photodetectors by 3D Self‐Assembly of Heterogeneous Nanoparticle Networks

Abstract

Accurate detection of ultraviolet radiation is critical to many technologies including wearable devices for skin cancer prevention, optical communication systems, and missile launch detection. Here, a nanoscale architecture is presented for band‐selective UV‐photodetectors, which features unique tunability and miniaturization potential. The device layout relies on the 3D integration of ultraporous layers of tailored nanoparticles. By tailoring the transmittance window between the indirect band gap of TiO2 nanoparticles and the sharp edge of the direct band gap of ZnO, a band‐selective photoresponse is achieved with tunable bandwidth to less than 30 nm and photo‐ to dark‐current ratios of several millions at a light intensity of 86 μW cm−2 and operation bias of 1 V. The potential of this integrated morphology is shown by fabrication of the first inherent UVA photodetector with selectivity against the edge of the UVB and visible light of nearly 60 times. This tunable architecture and nanofabrication approach are compatible with state‐of‐the micromachining technologies and provide a flexible solution for the engineering of wearable band‐selective photodetectors.

Recent Progress in Photonic Synapses for Neuromorphic Systems

“…Currently, ZnO with its unique visible‐blind ultraviolet‐sensitive detection has attracted great interests in designing photonic synaptic devices . Kumar et al first reported highly transparent synaptic devices based on all metal oxide, with structure fluorine‐doped tin oxide (FTO)/ZnO/In 2 O 3 , as shown in Figure a .…”

“…[70][71][72][73] Currently, ZnO with its unique visible-blind ultravioletsensitive detection has attracted great interests in designing photonic synaptic devices. [74][75][76][77] Kumar et al first reported highly transparent synaptic devices based on all metal oxide, with structure fluorine-doped tin oxide (FTO)/ZnO/In 2 O 3 , as shown in Figure 2a. [78] In addition to emulating major synaptic behaviors including STP, PPF, and LTP, they focused on realizing the impressive photonic potentiation and electrical habituation behaviors ( Figure 2b).…”

Nanoarchitechtonics of Visible‐Blind Ultraviolet Photodetector Materials: Critical Features and Nano‐Microfabrication

“…Wide bandgap semiconductors have been investigated in many recent studies to understand the fundamental process and enhancing the response to the UV light. [9,15,25b,40] The photoresponse characteristics of nanostructured devices are significantly influenced by a number of factors, such as the concentration of defects,[2d,3c] crystallographic orientation, bandgap, grain size,[1b,2d] and processing condition . These factors significantly influence the photoresponse behaviors explaining the large variation in performance previously reported by various groups for similar materials.…”

“…Many wide‐bandgap materials ( E g > 3.3 eV) have been investigated as building blocks for visible‐blind UV photodetectors, including gallium nitride (GaN), tin oxide (SnO 2 ), titanium dioxide (TiO 2 ), silicon carbide (SiC), and zinc oxide (ZnO) ( Table 1 ). [3c,9,15] Visible‐blind photodetectors based on GaN, ZnO, and SiC have raised particular interest for use in space communications, flame and missile launch detectors, and chemical sensors. [2a,b,d,16] However, despite these strengths, wide bandgap semiconductors often provide inferior charge carrier diffusion lengths, internal quantum efficiency, and electron/hole recombination kinetics than silicon resulting in a poor micro‐macroscale performance …”

“…Nanostructured wide bandgap UV photodetectors have been produced by several methods, such as magnetron sputtering, pulsed laser deposition, chemical vapor deposition, flame spray pyrolysis,[2d,9,15] and sol–gel . A critical aspect remains how to accurately control the composition and hierarchical arrangement from the atomic scale of surface and bulk defects to the microscale of the active device area.…”