Recent advances in development of nanostructured photodetectors from ultraviolet to infrared region: A review.

van der Waals (vdW) heterostructures based on two-dimensional (2D) semiconducting materials have been extensively studied for functional applications, and most of the reported devices work with sole mechanism. The emerging metallic 2D materials provide us new options for building functional vdW heterostructures via rational band engineering design. Here, we investigate the vdW semiconductor/metal heterostructure built with 2D semiconducting InSe and metallic 1T-phase NbTe2, whose electron affinity χInSe and work function ΦNbTe2 almost exactly align. Electrical characterization verifies exceptional diode-like rectification ratio of >103 for the InSe/NbTe2 heterostructure device. Further photocurrent mappings reveal the switchable photoresponse mechanisms of this heterostructure or, in other words, the alternative roles that metallic NbTe2 plays. Specifically, this heterostructure device works in a photovoltaic manner under reverse bias, whereas it turns to phototransistor with InSe channel and NbTe2 electrode under high forward bias. The switchable photoresponse mechanisms originate from the band alignment at the interface, where the band bending could be readily adjusted by the bias voltage. In addition, a conceptual optoelectronic logic gate is proposed based on the exclusive working mechanisms. Finally, the photodetection performance of this heterostructure is represented by an ultrahigh responsivity of ∼84 A/W to 532 nm laser. Our results demonstrate the valuable application of 2D metals in functional devices, as well as the potential of implementing photovoltaic device and phototransistor with single vdW heterostructure. 

/pdf/switchable-photoresponse-mechanisms-implemented-in-single-5lo2n4mz.pdf

Switchable Photoresponse Mechanisms Implemented in Single van der Waals Semiconductor/Metal Heterostructure

Co-Doped 3d Petal-Like Znin2s4/Gan Heterostructures for Efficient Removal of Chlortetracycline Residue from Real Pharmaceutical Wastewater

Co-doped 3D petal-like ZnIn2S4/GaN heterostructures for efficient removal of chlortetracycline residue from real pharmaceutical wastewater

The heterogeneous integration of low-dimensional materials with photonic waveguides has spurred wide research interest. Here, we report on the experimental investigation and the numerical modeling of enhanced nonlinear pulse broadening in silicon nitride waveguides with the heterogeneous integration of few-layer WS2. After transferring a few-layer WS2 flake of ∼14.8 μm length, the pulse spectral broadening in a dispersion-engineered silicon nitride waveguide has been enhanced by ∼48.8% in bandwidth. Through numerical modeling, an effective nonlinear coefficient higher than 600 m-1 W-1 has been retrieved for the heterogeneous waveguide indicating an enhancement factor of larger than 300 with respect to the pristine waveguide at a wavelength of 800 nm. With further advances in two-dimensional material fabrication and integration techniques, on-chip heterostructures will offer another degree of freedom for waveguide engineering, enabling high-performance nonlinear optical devices, such as frequency combs and quantum light sources.

Enhancing Si3N4 Waveguide Nonlinearity with Heterogeneous Integration of Few-Layer WS2.

Gallium nitride (GaN) was epitaxially grown on nitrogen doped single layer graphene (N-SLG) substrates using chemical vapour deposition (CVD) technique. The results obtained using x-ray diffractometer (XRD) revealed the hexagonal crystal structure of GaN. Photoluminescence (PL) spectroscopy, energy dispersive x-ray (EDX) spectroscopy and x-ray photoelectron (XPS) spectroscopy revealed traces of oxygen, carbon and nitrogen occurring either as contamination or as an effect of doping during the GaN growth process. In addition, PL revealed a weak yellow luminescence peak in all the samples due to the presence of N-SLG. From the obtained results it was evident that, presence of N-SLG underneath GaN helped in improving the material properties. It was seen from the current-voltage (I-V) response that the barrier height estimated is in good agreement with the Schottky-Mott model, while the ideality factor is close to unity, emphasizing that there are no surface and interface related inhomogeneity in the samples. The photodetector fabricated with this material exhibit high device performances in terms of carrier mobility, sensitivity, responsivity and detectivity. The hall measurement values clearly portray that, the GaN thus grown possess high electron contents which was beneficial in attaining extraordinary device performance.

/pdf/fabrication-of-gallium-nitride-and-nitrogen-doped-single-3mb4fuenny.pdf

Fabrication of gallium nitride and nitrogen doped single layer graphene hybrid heterostructures for high performance photodetectors

Van der Waals heterostructures are the fundamental building blocks of electronic and optoelectronic devices Here we report that, through a single-step chemical vapour deposition (CVD) process, high-quality vertical bilayer MoS2/WS2 heterostructures with a grain size up to ∼60 μm can be synthesized from molten salt precursors, Na2MoO4 and Na2WO4 Instead of normal pyramid vertical heterostructures grown by CVD, this method synthesizes an anti-pyramid MoS2/WS2 structure, which is characterized by Raman, photoluminescence and second harmonic generation microscopy Our facile CVD strategy for synthesizing anti-pyramid structures unveils a new synthesis route for the products of two-dimensional heterostructures and their devices for application

/pdf/single-step-chemical-vapour-deposition-of-anti-pyramid-mos2-2ae9zas0te.pdf

Single-step chemical vapour deposition of anti-pyramid MoS2/WS2 vertical heterostructures.

Enhancement of visible light photodetector performance for ultrafast switching using flower shaped gallium nitride nanostructures

Device fabrication using semiconductor nanostructures for detecting ultraviolet (UV) radiations, especially UV-A (320–400 nm) has received much attention both at laboratory level and in commercial endeavours. In this work, we have attempted catalytic growth of good quality gallium nitride nanowires (GaN NWs) for utilization in building high-responsive optoelectronic devices. In order to obtain good quality control in the growth of GaN NWs, single metal catalyst has been replaced with a binary catalytic alloy of gold-palladium (Au-Pd). Scanning electron microscopy (SEM) results revealed that the NWs grown are long, dense and uniformly thick in size. The hexagonal crystal structure of the grown NWs was confirmed using x-ray diffractometer (XRD) and transmission electron microscopy (TEM). Other characterization results like x-ray photoelectron spectroscopy (XPS), Raman spectroscopy and photoluminescence (PL) spectroscopy were helpful in determining the compositional and optical properties of the samples. The fabricated GaN NWs based UV-A photodetector showcased a fast rise time (τr) and fall time (τf) of around 22 and 29 ms, an ultrahigh responsivity (R) and sensitivity (S) of about of 11.87 × 107 A/W and 3.8 × 104%, an external quantum efficiency (EQE) of 9.45 × 109%, very high detectivity (D) of 3.83 × 1018 Jones and high wavelength selectivity in the UV-A regime.

Controlled growth of gallium nitride nanowires on silicon and their utility in high performance Ultraviolet‑A photodetectors

We demonstrate that thicker layers can be achieved in gallium nitride (GaN) epitaxy by using a patterned silicon (Si) substrate compared to a planar Si substrate. GaN films were grown by metalorganic vapour-phase epitaxy on 6-inch Si (111) substrates patterned with arrays of squares with various corner shapes, height and lateral dimensions. Stress spatial distributions in the GaN pattern units were mapped out using confocal Raman spectroscopy. It was found that the corner shapes have an effect on the uniformity of the stress distribution. Patterns with round corners were found to have more uniform stress distribution than those with sharp corners. The largest crack-free square size for a 1.5 μm thick GaN film is 500 × 500 μm2.

https://iopscience.iop.org/article/10.1088/2399-6528/ab885c/pdf

Ramesh Raju

Papers

Fabrication of gallium nitride and nitrogen doped single layer graphene hybrid heterostructures for high performance photodetectors

Single-step chemical vapour deposition of anti-pyramid MoS2/WS2 vertical heterostructures.

Enhancement of visible light photodetector performance for ultrafast switching using flower shaped gallium nitride nanostructures

Controlled growth of gallium nitride nanowires on silicon and their utility in high performance Ultraviolet‑A photodetectors

MOVPE growth of GaN on patterned 6-inch Si wafer